It's been about 18 months, since I even looked at a mac, but there is a built in sysinfo utility (somewhere), that will tell you what processes are running, and how much CPU they are consuming.
My G4 Powerbook started getting real sluggish, the fan stayed on all the time, and CPU utilization was maxed out.
Turned out to be the McAfee Anti-Virus. It had become corrupt, would launch, and then forever more, take up 75% of the cpu, forever.
Perhaps someone more knowledgeable about Macs can be more specific, but I think that this is probably the case.
Thanks. I found all of the system info EXCEPT the CPU readings. I guess I'll wander down the hall and ask the poor PC guy they hired to work on our iBooks where I find that information.