my computer wont shut down because of limewire HELP?

[Kait]

i have a mac, and i just downloaded the lastest version of limewire and the limewire wont even open... does anyone know why?
also when i go to shut down my computer it wont becuase the limewire thingy pops up at the top where it says what program im using, it highlights blue, and then the computer cant shut off!!
please does anyone know whats going on.
im going on a roadtrip in like an hour and i wanted to down load new songs before hand..