Personally, I'd still try loading a Linux Live CD and find out if it is indeed the hardware.
Sometimes, drivers are at fault which makes it a software problem. Also, the page file may also be taking up too much resources if control is left to Windows XP. I always keep my page file permanent and located in a different hard drive from where XP is installed. There has not been any sign of similar cpu spikes whatsoever.
With Vista, the page file is contained in the same 40gb hard drive where Vista RC1 is. I do keep it permanent as well.
Add: I'd also keep an eye on hard drive activity the next time the spikes occur.
Last edited by Jun aka Pekto; February 25th, 2007 at 02:56 PM.