Need Opinions/Help on a build I have put together

[mylitomutalisk]

So this will be my first time building a gaming pc while spending as little money as possible. Here are the items I have picked out:

Case: Sentey Black Box Series BX1-4285 v2.1 Black SECC ATX Mid Tower Computer Case
http://www.newegg.com/Product/Product.aspx?Item=N82E16811322038

Motherboard: MSI G31TM-P21 LGA 775 Intel G31 Micro ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130234

Power Supply: APEX AL-D500EXP 500W ATX12V Power Supply
http://www.newegg.com/Product/Product.aspx?Item=N82E16817154026&Tpk=APEX%20AL-D500EXP%20500W%20ATX12V%20Power%20Supply

CPU: Intel Celeron E3400 Wolfdale 2.6GHz 1MB L2 Cache LGA 775 65W
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116348

HDD: Western Digital 250GB 7200 RPM 16MB Cache SATA 6.0Gb/s 3.5"
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136771

DVD Drive: LITE-ON DVD Burner
http://www.newegg.com/Product/Product.aspx?Item=N82E16827106289

RAM: Mushkin Enhanced 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
http://www.newegg.com/Product/Product.aspx?Item=N82E16820146693

Video Card: XFX NVIDIA GeForce 9800GT 512MB DDR3 Video Card
I have picked this up locally for 40$.

O/S: Windows 7 Professional 64-bit (My Brother has an unused copy I can use)

Monitor mouse and keyboard I already have. Altogether, the parts I need would cost me $324.27 after taxes and shipping at newegg. Now, what I'm concerned about is if I picked out the right parts or not. I consider this a pretty cheap build for a gaming pc, and I have known friends who have spent around 600-800$ for a gaming computer that wasn't too fancy. I mainly want to run games like Starcraft 2, Diablo 3, and CS:S in high detail. If I bought all these parts and assembled the computer would I be able to run said games? Is a Mid-Tower good for gaming? (I've read that they don't provide enough ventilation for gaming computers)

Any help/insight would be very much appreciated. Thanks in advance!

[RickyTick]

This is a better case and comes with a better power supply, and is a couple of dollars cheaper than the case and psu you have picked out.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129065

I like this motherboard. The Intel LGA775 is 3 generations old now. It puts you in a dead-end.
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130560

Then add this cpu to it.
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103903

And then you can step up to DDR3 ram. Here's 8gb for $55.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231311

I think you'll find these to be more "bang for your buck".