Oops. Forgot to check the system specs tab.
Right: one PCI-E X16 slot. (It may not be PCI-E 2.0, but I believe that all PCI-E 2.0 cards are backwards compatible.)
I'd still suggest the ATI HD57xx cards. It probably isn't worth a price premium to get the latest technology, but I've noticed in the past that prices of the previous generation (HD4xxx) tend not to drop when the new tech comes to market. For example: a 4770 with a 750 Mhz core clock, 640 stream processors, and 512MB of 800 MHz memory at 800 MHz sells (
www.newegg.com) for about $110 and up. A 5750 with a 700 MHz core clock, 720 stream processors, and
1GB of 1150 MHz RAM sells for $145. That's not a trivial price difference, but the 5750 would be superior at higher resolutions, and it's DX11 as well.
I tend to prefer nVidia's
drivers, but I believe that ATI/AMD has the price/performance lead in hardware at the moment.
One caveat: I see that the OP's system board has onboard graphics. I hope there's a BIOS setting to disable that. I have read postings from people having trouble getting discrete graphics cards working properly in systems with onboard graphics that couldn't be explicitly disabled. A quick check online didn't reveal whether the system has such a BIOS setting.