Get a Intel Core Duo 2. The base model will outperform the highest brand AMD processor avaiable with just a little tweaking and is cheaper than the 4200+.

Personally i think 1GB is fine for most games, 2GB helps if you do play alot of MMO's or multitask alot.

GFX cards are iffy simply because the new chipsets are coming out this winter, so prices will drop on the current ones, meaning buying now will mean you will be able to get the same card much cheaper a couple of months later. As a rule of thumb ATI cards have a much better image quality and perform better in games like HL2 or Oblivion (anything that requires alot of shader grunt) and nVidia handles OpenGL better. I personally think you're best off with a 1900XT or a 1800XTX at the minute for a single card.

I don't know alot about the new Intel Mobo's, but i'm sure someone else here will.

Bottom line, get a Intel Based computer, the new chips are unreal in everyway.