Sounds like you have a worm. There's a fix here to try, it's worked for a lot of people. Click on the link below.
The easy fix for Limewire popping up every few seconds (try this first)
And more info here: WARNING: Viruses on network you should be aware of!

If you still need help, try one of the sites below...they're more specialised in helping with malware issues.

Spyware Warrior :: Index
CastleCops® » Security Forums
SpywareInfo Forum FAQ - SWI Forums
Malware Removal - MajorGeeks Support Forums

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