600 or lower gaming system

Hello I am going to be building a new gaming computer this August. This is my first build so it would be nice to include the prices of tools and stuff I will need. The system im looking to build isnt that hardcore a system. I would like to play most steam/valve games, WoW, and fallout 3.

PARTS I DO HAVE: All the basics such as mouse keyboard etc, 1440x900 Monitor and, ATI Radeon HD 4650 video card.
PARTS I NEED: Everything else.

Any sugestions on just the basics of building would be awsome.

Thanks for looking,
Crimsonshadow