Sounds like you have a worm. Try this fix, it's worked for a lot of people.
The easy fix for Limewire popping up every few seconds (try this first)

If that doesn't help, there are links to help sites below
Spyware Warrior :: Index
CastleCops® » Security Forums
SpywareInfo Forum FAQ - SWI Forums


Always make sure that you're using a good AV program. Keep it updated & use it to scan files that you've downloaded before you open them.