BACKPACKER Revision 3 of MediaEdit 3.0.1, released April 7 '08, finally works on my G4 with Leopard. Thanks.
BTW, as with v3.0.0, selecting Audio (on the right-hand-side of the Project window) consistently causes crashing if my USB-headphones aren't plugged in. It seems like M.E. remembers that I first tried it with the headphones, and now requires them for the Audio function always. Unplugging the headphones in Audio also causes the crash ('An exception of class NilObjectException was not handled. The application must shut down.')
(Version 3.0.1)