Doom 3 wasn't even intensive, I remember I could run it and it looked good on a 64mb GeForce 2 and 128mb RAM. Framerate was a bit choppy but it was perfectly playable. People just need to stop assuming their bargain Dell family PC was any good in the first place.
Do the research, learn about the hardware, build your own system. Save money and actually be able to play new games without them looking like shit. Hell, I only have an 8600 GT but I can still play most new titles in full detail, because I know what it's capable of.