According the the limited but decent System Monitor in Windows 98, I have discovered that moving my mouse decreases the Kernel: Processor Usage significantly. Let the computer sit idle and my processor reads at about 50-70% usage. Move the mouse around and it drops to to 10-30% range. Whats the deal?
It could be that there is a system process that kicks in when your computer becomes “idle” and this process has a low priority. Probably something like swapping pages of memory from disk to RAM. When you activate your mouse Windows focuses the attention of the processor to whatever application your mouse happens to be hovering over. When you return to an idle state the background process kicks in again working “behind the scenes.” It could also be a virus working in the background, but I’m sure you have good anti-virus software, don’t you?