Try this:

~/CLASSPATH=[path to rt.jar or classes.zip]
~/export CLASSPATH

and if it still won't work, check if you don't have multiple JREs installed on your computer, for if so, it might be that the wrong JRE is used by default.

Or you could simply download LimeWire without Installer (there is such a version for Linux) and unpack it into the archive you would like it to be.