I was planning to build one, but I would probably screw up. I changed my mind about the dell desktop I was going to get(I was attracted to it by its quad core and 3100 score on cpubenchmark), but I learned that graphics cards are more important for gaming(and the dell desktop was getting some bad reviews). I also need to know which ones are compatible with each desktop(based on power usage I presume since each desktop has an open pci slot).
Regardless, all of those GPU's are PCI-e, so as long as the desktop has a PCI-e slot any will work. Next you have to look off wattage, which I think is nothing more then 350W. Also none of those are too fantastic for gaming, so if you could tell us your gaming desires and budget we could help more.
Alright, the desktops are final though(only options). I'd say my max for a video card is $50 dollars(will use a $50 vista gift card). I won't be playing Crysis or games demanding as that. I'll play 2007-2009 games such as combat arms crossfire, SUN, Atlantica, and etc. My friend has a intel quad core Q6600/radeon 2400HD/2 gig ram, and he can play all these games without lag(all max settings). My laptop has a QL-64 dual core athlon/ radeon 3200HD integrated/ 4 gig ram(sucks so much. was great in beginning though. it had no lag on any game for 2 months), so this desktop will be godly compared to my laptop.
Off Topic: How do I make my links not dead? lol. I'm using firefox and the links work fine.
1st : asus CM5671-05 $500
2nd: gateway SX2801-01E $520