i build computers, but not for canada anymore. the import tax kicks the crap out of anything you save from buying through me.
get a system that's got at leasdt 2.6ghz of either intel or amd. it's gotta be at least a dual core. get at least 2 gigs of memory that's at least ddr2 533. get a graphics card that's an 8600, 8800, 9600, or 9800 (the first denotes the series of the card: 5 is bad, 9 is awesome. the second number denotes the quality of the card: 4 is lowest, 8 or 9 is the best). make sure the letters afterwords include G and T (gt, gtx, gtx+, not gs). if you're going with ati (radeon), get at least a 3850. make sure said graphics card is NOT agp, and that it has at least 512m of ram built in. NO INTEGRATED GRAPHICS. you want at least 250g of hard drive space, less is a ripoff.
that's a budget gaming pc. if you built yourself, i'd give you a list, but you obviously don't.
edit: tigerdirect is horrid for pricing. get a system from newegg, if you must buy premade.