It installs itself to run at startup. Go to Start > Run, type msconfig and press Enter.
Click on the Startup tab and look for Limewire in the list. Click to remove the tick and restart your computer. On restart a box will pop up saying you used the msconfig facility. Put a tick in the box so it doesn't come up every time you start up.
-------------------- OK OK I can't go any faster! aaaaaaaaaaaagh!