There are about 10 "build me a pc" threads started every week, so if you search you'll find plenty or info, and learn quite a bit in the process. Most people order their parts from Newegg , which has about the best prices and shipping.
Go to a computer site/store and ask for a system that THEY built.
but..
3500+ AMD 64 Venice core
1gb RAM
6800GT
250GB HDD
DVD Writer maybe lightscribe.