Processor working for no apparent reason

[Invizzible]

Hi all, I have an issue with Tiger 10.4.11 that I don't understand and I'm hoping someone here will have a fix. I'm running it on an ibook 900mhz G3, and menumeters shows that the processor is constantly fluctuating anywhere from 1% useage to about 70%. This is while the computer is just sitting there doing nothing, not even moving the mouse. I opened up the activity monitor and I see that the dock is using anywhere from 0% processor to about 30%, and something called Windowserver is also sometimes hitting about 30%. Can anyone tell me how to fix this? The ibook runs so hot that sometimes it freezes, other times it's very slow due to limited remaining cpu power. Would it help to do an 'archive and install' reinstallation of OS X? Is there a fix w/out going to that trouble? I don't know enough about computers to really understand what's going on. Here are a couple screenshots of the activity monitor window: