Are you bringing anything to the build (Case, power supply, video card, etc) or is it a build from scratch? If so then list what you want to take over to the new PC. I would hit
http://www.newegg.com and start building. If you need a case then I would look at the Antec's as you get a good case and power supply together. I would actually look at a AMD processor as you can usually get more bang for your buck. Socket 754 (Athlon 64) processors are cheap and you can still get good performance from an AGP video card. The 6600Gt is your best bet for 150.00 but the ATI 9600XT and 9800Pro aren't bad cards either.
Edit... NVM