AMD was the best for gaming until the core 2 duo came out. Bottom line is intel won and is going to be better in the future as well as the present. the 775 socket will be a much better choice for upgrading in a year or even 2. The AMD x2 4200 is already AMD's second best processor. If they change their socket ( which the will have to sooner or later for better performance ) you are only going to be able to upgrade to one level higher. With intel in 2 years from now the quad core you can get today will still rock and it uses the same socket as the e6600. Of coarse if you change your cpu you must also change the motherboard as well. It will eb a bit more but the Evga 680i sli is by far the best choice (especially if yoru planning on useing the evga 8800 gtx. If your strong on amd though maybe look into ati for your gpu, i hear they work better together than nvida and amd. Plus you will save like 300-400 and have the same perfrmance.
Evga nForce 680i sli Motherboard
Apevia Blue X-Cruiser Case
Dell UltraSharp 2408WFP-HC Monitor
Logitech Z-5500 5.1 Speakers
Logitech G5 Mouse