Try disabling ultrapeer. If that doesn't help, I would highly recommend downloading jum's build of LW at http://baghira.han.de/~jum/. Download the file that starts with Limewire, mount the disk image and just drag it to your harddrive. It drastically reduces CPU usage, memory usage, as well as certain problems where OS X users have had it crash when it's up for long periods of time.