Reader “Hal” asks: “Is it possible to save an iDVD theme as a QT file, such that it can then be imported into iMovie and used as ‘bumper’?”
Unfortunately, unlike iMovie’s new Quartz themes, most of iDVD’s themes seem to remain in the old Oxygene format (pox folders, containing Oxygene patches and the media that support them). You can hack out a few of the pieces, but it ain’t pretty and it ain’t trivial. Probably your best bets are: 1. use the new iMovie 6 themes instead, 2. wait for iDVD 7 which will probably be ported to Quartz or 3. build ‘em yourself in Quartz Composer.
Other more hacky approaches include using Snapz Pro to capture the video as it plays in iDVD or to grab the MPEG-encoded video from a DVD disk image produced by iDVD. Be aware that you’ll probably need to pay Apple for an MPEG-2 license to be able to edit and use MPEG-2 source in iMovie.