I'm still leaning towards a configuration problem. I had similar difficulties on one of my Macs at one point where Terminal would quit on launch, and it turned out to be a problem with how I had configured the app. Unfortunately, I can't quite remember just what the problem was and how I fixed it.

What exactly is the error that is displayed when you launch the Terminal app? Can you ssh into the Mac remotely?

Peace,
Drew
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Power to the PowerPC!