Trash your prefs. And throw out that xvid file for sure. If you copied all your Library files over from your G4 then you have a lot of non-Intel files.
If you can't get it to work, I might suggest you try creating a new user account and see if FCP will launch from there, without any of the baggage from your current emigrated account. Start clean.
JK
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SCQT! Self-contained QuickTime ? pass it on!