yeah, I was going to suggest the gt 9800 (which is pretty good), but the ati card mentioned above would be better and they are a similar price.
I can't find anything related to your motherboard on internet... Tell us, what version of pci-e slot? 1.0? 1.1? 2.0? 2.1?
1.0 (I think?)
How do I find out?
For the safest way, get 9800GT Green Edition (doesn't required 6pin power connector), your PSU should be fine to handle that card... Any card above that will be wasting money...
I wouldn't trust anything more than a 5570 or 5670 on that power supply.
the newest 9800GT will not consumes lot of power, cause it will draw power from pci-e slot on motherboard... Yes, HD5670 is better, but his mobo only has pci-e 1.0 slot, so i think he will better with pci-e 2.0 card, like 9800GT.