Powerbook G4 (kernel_task CPU Usage)

Hi.

When I connect to the internet, my Powerbook suddenly starts to use anything up to an average of 40% of my CPU. Also, it quite often causes CPU spikes, thus meaning that near-to or exactly 100% of my CPU is used up for a split second, and then it will drop down, varying from on average anywhere between 26% and 52% usage (some times higher).

Once I disconnect from the internet, my CPU usage drops back down to normal. Just to note, this is SYSTEM CPU usage, not USER, and it seems to be a task called 'kernel_task' that is using it (which I'm presuming is the core of OS X).

Can anybody shed any light on this? Any fixes?

Thanks,
onlyone-jc.