This may be valuable to your readers having trouble with the iDVD 7.0.3 update. Here's the scenario: A whole lab of machines imaged from the same valid, clean installation of Mac OS X 10.5.6 and a working iLife '08 installation suddenly all refuse to make DVDs with iDVD after the 7.0.3 update.
It turns out that there is something wrong with the iDVD 7.0.3 update, and the problem is observable on Intel and PowerPC systems running Mac OS X 10.5.6 and QuickTime 7.5.5 or 7.6. When attempting to add a movie file of any format (m4v or mov, for instance) to a new iDVD project or One Step DVD, iDVD 7.0.3 refuses to accept it, saying that the movie is an "unsupported format" or "unsupported file type."
Reverting to iDVD 7.0.2 corrects the problem, but as far as I can tell, the heart of the problem is in the iDVD executable itself (iDVD.app/Contents/MacOS/iDVD), so the rest of the 7.0.3 update should be just fine. Here's a procedure to keep the rest of the 7.0.3 update while downgrading the iDVD executable to version 7.0.2. This procedure is superior to simply restoring a 7.0.2 version because you get the "good parts" of the 7.0.3 update and Software Update won't remind you of (or automatically download) the iDVD 7.0.3 update, because it thinks it's already installed.
Read the rest for the how-to...
Here's what I did to downgrade the executable:
$ sudo mkdir /tmp/iDVD702-update
$ cd /tmp/iDVD702-update
$ sudo pax -r -p e -f /tmp/iDVD702.pax
Now the iDVD 7.0.2 update pieces are in /tmp/iDVD702-update. Mac OS X Hints
http://hints.macworld.com/article.php?story=200902031209456