don't know the us prices and especially teh system with all tehse Mail in rebates makes it hard to get a good overview.
but for teh equivalent of 700€ which is about ~$1000 i would probably aim for a intel core 2 duo 8400 (maybe even an 8500, 8600 is most likely out of the price range) and a ati(amd) 4870 combination. together with mainboard (i would get one with intel chipset), ram (4gb ddr, but can also settle with only 2gb), 500gb harddisk (can get bigger if you got enough money left), a medium quality case and a good 500W psu you should probably get close to that price