First, uninstall LimeWire, then get a virus scanner and run it over your system. You have infected yourself with a worm by downloading something from LimeWire (possibly an .exe, .pif, .vbs or .wmv file). The worm spreads itself via your LimeWire shared folder and will always try to start LimeWire.

More info:
http://www.gnutellaforums.com/showth...threadid=39552