Hmm. Well, yeah you can get a Bot with at least 1GB, an ATI X700 or a 5300 with 1GB, and an ATI X300 for acceptable performance on HL2 and Doom 3. And when I mean acceptable I mean playable at not very high resolutions (most probably the games will switch to 640X480 or 800X600) and most of the goodies like AA, AF and water, reflections, shadows, fog, particles or whatever the game has turned down to low or middle settings or completely turned off.
Of course, current AW pricing is after mail-in rebates so listen to solar_eclipse and save up a little bit more. I know what it feels wanting to have something now and have barely enough money to get it but you'll be glad that you were able to order something a lot better by saving up some more.