Here are the things that I have tried, and what worked:

1. Installed from the Linux rpm. This is where the problem originally occurred.
2. Installed using the 'Other' distribution zip. Again had the problem.
3. Google'd the liquid look-and-feel that the exception description described. Found it at sourceforge, and downloaded it. Installed it in the place where I had unzipped the LimeWireOther.zip. The same problem occurred.
4. Tried to manipulate the runlime.sh file to add the liquidlnf.jar file to the path. Since the runlime.sh starts using the -jar option, I couldn't get it to work by adding a '-cp liquidlnf.jar' to the command line. I'm sure there must be a way to do this, but I didn't have the patience to fiddle around with it.
5. Downloaded the source and unzipped it. Copied the liquidlnf.jar to the proper location in the source directory. Went to core and did 'ant', and went to gui and did 'ant'. Then executed the 'run' script. The program started just fine.

It is clear to me that both the linux rpm and the LimeWireOther.zip did not have the required liquidlnf.jar file. For the LimeWireOther.zip, I searched in all the jar files and did not find the class files for liquid.

My conclusion is that the build process leaves out the bundling of the liquid look-and-feel jar with the distribution.