Would it be possible to modify JUnit so when "java -jar junit.jar -version", it prints the version out.(I would be happy with java -jar junit.jar printing out the version also. 
I do this with mockobject.jar.  Basically, I put the version information in the manifest file(under implementation version).  I then retrieve it from the manifest file with the Package class.  This can be all automatically done with ant1.6 and it's manifest generation quite nicely!!!
I would be happy to supply the code.  I typically then deliver the jars as junit.jar.version as the first thing people do is rename junit-version.jar to junit.jar so when they stick it in their repository, it is not creating a new entry every time(like CVS typically does).