But if you are going to play games, you might as well upgrade your rig if money is no matter. And tell me the type of RAM you have. (For eg: DDR, DDR2)
You may even consider getting a new mobo or a complete overhaul.
If you lived in australia i could literally give you a much better computer for free. Something that old is not worth spending money on, most people are throwing them away. You can normally find government auctions or something and pick up a much better entire system for $100, like a dual core p4 with 2gb ram or something.