The gateway one's only $500 though, including Windows 7 OS. Though there's no motherboard/power supply info supplied, which makes me a bit questioning towards it. I'll call em up tomorrow and find those out.
It's most likely a crappy OEM board. If you're not looking at any options for overclocking, an OEM board would be acceptable. Power supply is also probably sub-par, which won't do much good, if you're looking into upgrading the graphics card in the future (which for the games you want to play, it would probably be necessary). The GT120 is not a gaming card. As stated you want atleast a 9800GT (Nvidia) or 4830 (ATI). I have a 9800GT, and have some problems with newer games... The 9800GT is far FAR better than the GT120.