Windows suffers from a similar problem with Java, which was where I got the idea to try this.
A Jar file is just a compressed set of Java classes. You can invoke them in the terminal via java -jar, just like if it were a class.
The LimeWire "app" that you see *kind of* does the same thing.
Anyways:
1. Open Terminal
2. Type "java -jar " and drag in the file "LimeWire.jar" in the LimeWire folder.
i.e. "java -jar /Applications/Limewire/LimeWire.jar"
LimeWire will now start up.
DO NOT quit Terminal, and try to live with the fact that instead of the LimeWire icon in the dock, you get Apple's generic Java Application icon.
What was using 70-80% on my dual 1Ghz is now using between 5 and 20.
Have fun!
Mike