This is the simple case. If you've got a 1.2 jvm installed:
java -jar jskeleton.jarshould do it.
Windows
Windows + java 1.2 should allow you to double click on the jar file. This worked for me with jdk 1.3.
1.1.x jvm
I don't think JSkeleton actually runs in 1.1.8 anymore. Use 1.3.