Tasy,
You really don't want to do that.
If you are running Panther, I recommend updating Java via Software Update or going to
http://www.apple.com/downloads/macosx/apple/java.html . If you're running Jaguar or whatever 10.1 is called, I recommend re-installing LimeWire.
I have absolutely no clue what side-effects changing LIME to LimeWire will have, but I do not think they're good.
Thanks,
Sam