New card in old PC Questions

[TTDiver]

I've got an older HP media center m7690y and I'm interested in replacing the Nvidia GeForce 7300 Le video card, mostly for Diablo III and Starcraft II game play. I'm very new at this, but I've been trying to do my research. I'm looking at the Nvidia GTX560, but want to make sure what I'm doing will work and that it makes sense.

Intel Core 2 CPU 6400 @ 2.13 Ghz
4GB DDR2 SDRAM
Windows XP
Existing PSU 350W

It looks like I need to replace the PSU with something in the 500W range. I'm fine with that. Any suggestions?
The 7300 is PCI-e x16 which should be compatible with the GTX650, right?
The existing card is 10.35" x 6.41" x 2.36, but I'm finding it difficult to find the numbers on the GTX.

Will this card be bottlenecked by my CPU?
Will it fit?
Is there anything else that might cause a problem that I haven't thought about?

Thanks a ton.

[RickyTick]

The GTX560 is about 9 inches long, so it should fit easily.
Yes, the cpu will be the bottleneck it that setup, but most modern games are gpu bound anyway, so it may not be a very big deal.
There are several good power supplies in the 500-600 watt range. Look for brands like Corsair, Seasonic, or Antec.

[TTDiver]

Thanks for your feedback. I haven't thought about updating the CPU. Any idea what the motherboard could handle. It's listed as a Basswood P5BW-LA.

[RickyTick]

If you think you may replace the cpu also, then you might as well build a completely new system.