Did you unistall XP home off your hard drive before you installed XP pro....this happend to my mom and her dekstop was exteremly sluggish.
Also what do you use this computer for......If you can I suggest you bring your computer to your local computer store and ask them if they can install you a extra 256 MB of ram. You will see a noticable performance increase
Also when I move around my browser My cpu hits 70% somtimes too
but then again I have a pentium M...(still waiting for part to finish other computer)