This got me thinking whether the same is true of the other Apple Pro apps, and as I found, in the case of both Soundtrack and Compressor, it certainly is. To make the apps run on a crappy old G4, here's what you need to do. Control-Click the app and select Show Package Contents. Open the Contents folder. Open the info.plist file. The easiest way to do this is if you have the Property List Editor installed (from the Developer Tools), but BBedit (or any other pure text editor) should do fine. Find where it says Graphics Card Required and simply change AGP to PCI. Save the file.
This hack allows both FCP4 and Compressor (you have to repeat for both apps) to run perfectly well on a Yikes G4/400 (albeit with 640MB RAM), and if you don't mind renders that take a while, it makes both apps perfectly usable.
To get Soundtrack (and the Soundtrack Loop Player) to work on my machine, I had to edit the Required Speed field to read 400 -- Apple suggests 500MHz minimum for running, but again I managed to get Soundtrack to run perfectly well with a few layers of sound on my 400mhz machine ... just by changing the preferences!

