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 ?
Comments and responses
18 Aug 2003
cool!! thanks for the tip.
14 Sep 2003
What isn’t cool is when you buy a new Power Mac G4 two weeks after iDVD 3 is announced, have a superdrive, but Apple wants fifty dollars for iLife or twenty dollars for “shipping” for software you’re entitled to have. Am searching the net once again trying to find someone who has posted iDVD 3.0 to which he’s legally entitled. Frustration.
16 Nov 2003
This might be a question you have been asked, but I have not yet found a 100% direct answer…
I have a G4 MAC running Final Cut Pro 3.0.4 on OSX and iDVD on OS9. I recently purchesed iLife, (for the iDVD 3 upgrade). Since buying (and waiting to receive it) I’ve been reading about needing a “superdrive” How do I know if my Mac G$ has one? I have been burning iDVD 1 without a problem. Is it safe to assume I have it built in or how can check? Thank you in advance for your help!
Shane
16 Nov 2003
This might be a question you have been asked, but I have not yet found a 100% direct answer…
I have a G4 MAC running Final Cut Pro 3.0.4 on OSX and iDVD on OS9. I recently purchesed iLife, (for the iDVD 3 upgrade to run on OSX with Jaguar). Since buying (and waiting to receive it) I’ve been reading about needing a “superdrive” How do I know if my Mac G4 has one? I have been burning iDVD 1 without a problem. Is it safe to assume I have it built in or how can check? Thank you in advance for your help!
31 Aug 2005
I have the 2002 quicksilver g4 model.
I recently lost my dvd superdrive so i purchased a newer external firewire Lacie lightscribe DVD burner. Now i cannot open my IDVD because I do not have the superdrive connected.
I a running system os 9.2.2 what should I do?