I'm using a Compaq R4000 laptop (see specs in sig.) quite a beast.
I have been experiencing the spikes since 5.0.1.
yesterday I optimized my laptop with these guidelines:
http://www.pcaudiolabs.com/winxp_tweaks.asp?cat=setu
i turned off my LAN and Wireless services as well.
at your own risk, try this tweak and see if it improves the spikes.
so far so good for me. Live feels more stable now.
i may have just jinxed myself.