Weeeeeeeeeeeeeeeeelllllllll....
If you'd post what you're going to be doing w/ this computer, we might be able to help you more. Also, a price range is helpful!
But...if you're going to get a new processor, more than likely you'll have to change your motherboard and ram as well. That means big bucks. However, you can get a nice Athlon XP or Intel P4 system that should last you a while. Via's C3 processor is another alternative...although it's considerably slower than it's competitors. Runs cool though. With either the Athlon or P4, you're better off running in the middle of the pack...i.e. 2000+,2.0 Ghz, or 2.2 ghz...cause that's where the price sweet spot's at right now. For now, update us on what you need. Don't forget that video card either...