To save time finding out what it is and getting rid of it etc etc... I'd just do a CLEAN install (reformat first) and install a firewall & antivirus software (zonealarm & AVG are both pretty good and free) BEFORE you go on the net. Then go to Microsofts website and download all the patches, it will download a package of everything for you.
Don't forget to have your security software ready on a disk before you reformat.
You can't last 5 minutes on the internet without security these days.
 Oh, and do a virus scan of any files that you may be copying back over after you re-install, maybe there's a virus on them.
do a format, install xp and install all the drivers and nothing else, what does the cpu time say?install each of your programs 1 by 1 until you find the one that is zaping your cpu, that and mabye more is the ones to kick.