Yeah, the OSX problem makes sense. OS X needs a native wrapper to start Java applications as .app, and we upgraded ours to a 'universal' one sometime during 0.8 development. Obviously, universal means 'everything but older versions of OS X', which we weren't aware of.
I don't think we'll integrate a fix in muCommander, it will mean having two different release files for OS X, reworking our build and deployement system, ... all for an OS that's virtually dead.
On the other hand, we *will* post a '10.2 HOWTO' on this forum, so that people in your situation can use the .app file. It's basically 'download JavaApplicationStub from here, copy it to /Applications/muCommander.app/Content/MacOS, restart muCommander'. We just need to unearth the right JavaApplicationStub version before we do that :)