i HAD THAT SAME PROB.
it's funny how different things work for different people/computers. Here's how I solved it.
First I tried the suggestions mentioned by others and got nowhere.
For xp pro
First-- open task manager control/alt/delete keep it open
(note which services are using memory and cpu.)
(some you don't even need like p2p networking - this come installed with kazaa but kazaa does't need it to work- you can uninstall at cotroll panel add/remove programs) and so on.
Second--open control panel/admin tools/services (not component services just plain services.
NOW arrange both windows so you can see them.
now go down the list of services and turn them off and back on while monitering the taskmanager until you see the culprit that is hogging your cpu usage.
note: my culprit happended to be "ssd discovery services" which was indicating it was "stopping" where the others read started.
HOPE THIS HELPS