The only compatible processors with that board I can find are P4s and Celerons, so there is not much upgrade room.
I did find that it can support up to 3.6 GHz though, so if you can find a Socket 478 P4 with 800 MHz FSB with anything up to 3.6 GHz, you should be good to go. I don't see the need for upgrading that though unless you have something that is a lot less.