Believe it or not, this is relatively simple to exorcise.
First, disable system restore if you're running XP or ME.
Then, do the following:
Go to Start > Settings > Control Panel > Double click your Java icon > find the Cache tab > click Clear JAR cache
That shoudl be the end of it.
"'Tis an ill wind that blows no minds." - Malaclypse the Younger