Stupid bloody explorer ate my post.
Heres a brief summary of its contents:
Zap your PRAM (apple-option-p-r at startup and let go after the third chime) and rebuild your desktop (apple-option as the Finder loads).
Can't hurt to delete the Finder and System preferences either.
Have you installed anything recently?
Did you notice this after installing something?
If you think its the MS libs, have you removed them and tried running?
Do you have anything like dnetc, SETI@home, et al running?
Anything that grabs idletime?
Do you notice this all the time, or only sometimes? If the latter, what apps are running?
You'll probably need to sort your extension list. Boot from a "Mac OS All" set (via the extensions manager), and reboot.
Problem gone? Good, sort your "Extensions (Disabled)" by date and about half at a time, move the items back to the Extensions folder. Reboot. Prob still gone? Great. Do that again. Half again.
If the problem has manifested itself, then you know that the culprit is somewhere in the group you just enabled. Narrow that group down and kill the problem.
Just a tip, using Finder labels could really help organise things here too.