I quite accidentally fell on this piece of valuable news this weekend while building a iDVD project: you can run iDVD on a G4 without a SuperDrive installed.
iDVD 3.0.1 KB article says just that
Starting with version 3.0.1, iDVD can be used on any Macintosh computer with a PowerPC G4 or G5 processor to create DVD content. However, the option to burn the finished DVD is only available on computers with a built-in SuperDrive. iDVD 3 may be included with your computer, even if it does not have a SuperDrive. 
Cool, no ?
