|Your CPU temporarily going up to 100% is normal as long as it drops down again when you close the offending program, especially with a single core like the P4. For better performance, make sure your Flash Player, Java, are the latest that supports XP. Do a Windows update to make sure you have everything up to date. Shut down programs you do not need running. Uninstall programs you never use. Remove most programs from starting with Windows. Do a disk clean up. Do a Hard drive Defrag. Clean out your browser's Cookies, History, Temp Internet Files, etc (repeat weekly). Set your browser to delete cookies and history when you close it.|
Taken all together, these should help. A new Windows 7 system with at least a dual core processor would help even more.
You have to be a little bit crazy to keep you from going insane.