See if updating Java helps. Use the JRE offline installer & remove any old Java versions before you install the new one.
http://java.sun.com/javase/downloads/index.jsp

You could also try using the Beta version of LW, that's helped a few people with CPU useage issues.
http://www.limewire.com/english/content/download.shtml

You could also disable ultrapeer capabilities (tools > options > speed, or in the Beta tools > optoins > advanced > performance).