Those aren't what you would call "newer" games. COD 4 has been out for what, like 4 years? All I know is, about two years ago I was looking at new games and decided then that my P4 wasn't going to do what I wanted anymore. I made the leap to a quad core and have never looked back. If you've got a decent monitor, you can build a pretty decent dual core gaming box for about $500. Is your video card PCI or AGP?
There are also a whole bunch of games out there. It would probably help if you gave us some sort of idea of what type of games you like to play?