Is this behaviour something that has changed since the laptop was new, or is it a new phenomenon?
The computer is quite old. so there is a possibility that it has accumulated a lot of dust which would cause it to run hot.
Another possibility that occurs to me is that it is quite a low spec machine, is it really up to running XP Pro - how much memory does it have?
You say that the CPU graph is all over the place, have you scanned for virusses and malware?