See if updating Java helps. Try uninstalling your Java from the add/remove programs and then re-install the JRE offline version....(4th one down)
Java SE Downloads - Previous Release - JDK 5
You could also try using the Beta version of LW, that's helped a few people with CPU useage issues.
Lime Wire » Download LimeWire
You could also disable ultrapeer capabilities...Go to Tools > Options > Speed, or in the Beta...Go to Tools > Options > Advanced > Performance....
Also here is another link to have a look at...
http://www.gnutellaforums.com/245000-post2.html