Uhh, actually cache and regisrty contents are in "Documents and Settings" not in Windows folder, So I agree with the others in that you need to do some heavy duty cleaning of the HDD.

I personally like to backup all my critical data and do a fresh OS install once a year, just to make sure of things, especially since 99.99% of all programs leave traces all over the place even after being uninstalled. (Why is it called uninstall if it doesn't actually uninstall??)