$800 for a gaming PC? I don't think that much was needed for a long time, unless you had to play the latest game on your 2600" screen with a high resolution.
For roughly $300 these days, you can build a machine to play any game you want on a 19" screen. You don't really need anything more than a GeForce 9 (~$100), and a high end X2 (~$60). The other ~$140 is more than enough to get some RAM, hard drive, dvd burner, motherboard, especially if you find a deal on newegg or the like.
This
here which is quite a decent machine is only $287 ($322 before rebates). Just add a DVD burner for ~$25, and you're all set.