Rookie needs help buying parts for/building new PC

[Singularity]

Hello everyone
After experiencing some problems with my current PC, as well as performance issues experienced when playing games (most notably and recently, The Witcher 2) I have decided to build a PC from scratch due to recommendations from friends and some positive experiences from other people online. Although I say from scratch, there are certain parts I may be able to salvage from my old PC, I'm planning to use my HD Radeon 5850 which I bought about 2 months ago (full info below)
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Display Devices
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Card name: ATI Radeon HD 5800 Series
Manufacturer: ATI Technologies Inc.
Chip type: ATI display adapter (0x6899)
DAC type: Internal DAC(400MHz)
Device Key: Enum\PCI\VEN_1002&DEV_6899&SUBSYS_21E41458&REV_00
Display Memory: 753 MB
Dedicated Memory: 1010 MB
Shared Memory: 3839 MB
Current Mode: 1920 x 1080 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: W2253
Monitor Id: GSM56DC
Native Mode: 1920 x 1080(p) (59.934Hz)
Output Type: DVI
Driver Name: aticfx64.dll,aticfx64.dll,aticfx64.dll,aticfx32,at icfx32,aticfx32,atiumd64.dll,atidxx64.dll,atidxx64 .dll,atiumdag,atidxx32,atidxx32,atiumdva,atiumd6a. cap,atitmm64.dll
Driver File Version: 8.17.0010.1077 (English)
Driver Version: 8.850.0.0
DDI Version: 10.1
Driver Model: WDDM 1.1
Driver Attributes: Final Retail
Driver Date/Size: 4/20/2011 02:07:48, 795648 bytes
WHQL Logo'd: n/a
WHQL Date Stamp: n/a
Device Identifier: {D7B71EE2-2BD9-11CF-DD73-EE01BEC2C535}
Vendor ID: 0x1002
Device ID: 0x6899
SubSys ID: 0x21E41458
Revision ID: 0x0000
Driver Strong Name: oem15.inf:ATI.Mfg.NTamd64.6.1:ati2mtag_Evergreen:8 .850.0.0:pci\ven_1002&dev_6899
Rank Of Driver: 00E62001
Video Accel: ModeMPEG2_A ModeMPEG2_C
Deinterlace Caps: {6E8329FF-B642-418B-BCF0-BCB6591E255F}: Format(In/Out)=(YUY2,YUY2) Frames(Prev/Fwd/Back)=(0,0,1) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{335AA36E-7884-43A4-9C91-7F87FAF3E37E}: Format(In/Out)=(YUY2,YUY2) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_BOBVerticalStretch
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(YUY2,YUY2) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY
{6E8329FF-B642-418B-BCF0-BCB6591E255F}: Format(In/Out)=(UYVY,UYVY) Frames(Prev/Fwd/Back)=(0,0,1) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{335AA36E-7884-43A4-9C91-7F87FAF3E37E}: Format(In/Out)=(UYVY,UYVY) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_BOBVerticalStretch
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(UYVY,UYVY) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(YV12,0x32315659) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{3C5323C1-6FB7-44F5-9081-056BF2EE449D}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,2) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{552C0DAD-CCBC-420B-83C8-74943CF9F1A6}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,2) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{6E8329FF-B642-418B-BCF0-BCB6591E255F}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,1) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{335AA36E-7884-43A4-9C91-7F87FAF3E37E}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_BOBVerticalStretch
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC1,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC2,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC3,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC4,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(S340,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(S342,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
D3D9 Overlay: Not Supported
DXVA-HD: Not Supported
DDraw Status: Enabled
D3D Status: Enabled
AGP Status: Enabled

As well as possibly, my RAM, I couldn't find out much information about it other than this: 8192 Megabytes Usable Installed Memory

Slot 'DIMM0' has 2048 MB
Slot 'DIMM1' has 2048 MB
Slot 'DIMM2' has 2048 MB
Slot 'DIMM3' has 2048 MB
Yeah not much to go on, I'll run memtest to make sure its all good, I also have an SB Audigy sound card which I'm planning on using as well, since I've had bad experience with integrated sound. I'll post my current PC specs if you want to see if I could use anything else, I dobut I could though.
Operating System: Windows 7 Professional 64-bit (6.1, Build 7600) (7600.win7_gdr.100618-1621)
Language: English (Regional Setting: English)
System Manufacturer: System manufacturer
System Model: P5QL PRO
BIOS: BIOS Date: 07/01/09 17:37:27 Ver: 08.00.14
Processor: Pentium(R) Dual-Core CPU E6300 @ 2.80GHz (2 CPUs), ~2.8GHz
Memory: 8192MB RAM
Available OS Memory: 8192MB RAM
Page File: 1736MB used, 14643MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7600.16385 32bit Unicode

Anyway with all that out of the way I should probably tell you what it is exactly that I'm aiming for, as well as my budget and experience. The rig I want to build is going to be designed for gaming, not neccesarily state of the art but I want to be able to run current-near future games on medium-high settings, my budget will be around $500-$800. My current experience in building PCs is, well... zero, but I am willing to learn and good at following instructions, the most I've ever really done is pop open a PC and install/replace GPUs and RAM, If there is a guide you recommend I read post it and I will, or else I will use the resources from this site.
OK, so I have done a little research and have a basic idea of what I want, however bear in mind my experience is limited/non-existant and my knowledge minimal. I was thinking of getting an intel core i7 2600 quad core which runs @ 3.4Ghz, price ranges from about $300-$350, expensive I know, but I think I can work with that, somehow.
I found an 860W PSU for about $60, which I plan on getting unless someone else says otherwise. Specifications:



Type
ATX12V

Maximum Power
860W

Fans
1 x 120mm, 2 X 80mm

Power Good Signal
100-500ms

Hold-up Time
>=10ms

Efficiency
>=70%

Over Voltage Protection
Yes

Over Load Protection
Yes

Input Voltage
230V AC

Input Frequency Range
50/60Hz

Input Current
4A @ 230V

Approvals
CE FCC C-Tick

Connectors
1 X Main Connector (20+4 pin)

1 X CPU 8(4+4) pin

6 X SATA Power

3 X IDE Power

2 X PCIE 6 pin

1 X PCIE 6+2 pin

1 X Floppy Power

Hard drive isn't especially important in terms of size, I was thinking between 400G-1TB, and for the motherboard, I have no idea what to get, of course it would need to be compatible with the GPU and CPU and having USB 3.0 would be a plus, and I was thinking of getting a Coolermaster case for about $100+.
Sorry for the mass amount of information, but the more the merrier right?
Anyway, I'm open to any and all opinions

[RickyTick]

Re-using the Radeon 5850 would be ok, but it's not a very powerful gpu and would struggle with new games like BF3, Crysis 2, ME3, Rage, etc. You should consider a Radeon 6950 or nvidia GTX560 Ti.

Your old ram is DDR2 ram and will not be compatible with new motherboard. However, ram prices continue to fall. You can easily get an 8gb kit for under $100.

That power supply is rated at 70% which is fairly low. You should be looking at one that is certified 80%+. You shouldn't need anything higher than 650 watt.

[Singularity]

hhmmm, so I should consider the HD 5850 as a temporary fix?
and I suppose I could easily buy more ram and vie for the i5 2500 rather than the i7 2600, from what ive heard there isnt much difference between the two (other than price)
The main problem I'm having is choosing a suitable motherboard, will it affect the speed of my system?

[RickyTick]

Speed is not really an issue with picking a motherboard. You should be looking at "features" and "price" more than anything. For your price range, you should be looking at a P67 motherboard. Something like this. http://www.newegg.com/Product/Product.aspx?Item=N82E16813131705

[Singularity]

Alright so, ASUS P8P67 - $150
Intel i5 2500 - about $230
found a decent coolermaster case - $110
860w PSU - $60
then I will need to get RAM, HD, ect...
I guess budget is looking ok so far, I might ask some of my friends if they have any spare parts I could use.
One more thing, if I use my HD 5850 for the time being, would it be a viable option in the near-future to purchase another 5850 for crossfire?

[RickyTick]

Having 2 5850's in crossfire would be like having a single 5970. If you could find a 5850 like the one you have at a decent price (think ebay), it would make a decent setup until you could save up the money to purchase something better like a 6950 or 6970.