|As mentioned, you need to look up the specs on your system or motherboard and find the CPU support list.|
I also agree that the first thing you need to do is to upgrade your memory to 1GB (1000MB) and you will notice a significant improvement. When your system was built 250MB RAM was minimum and 500MB was acceptable, but with improvements in antivirus software and internet browsers, 500MB is below acceptable for XP, it really needs quite a bit more.
If a memory upgrade does not help enough, save the money and consider replacing the entire system. Some of the lowest priced systems today can blow the doors off a P4 era system any day.
You have to be a little bit crazy to keep you from going insane.