I recently discovered a way to make iDVD '08 render multiple projects to disk image files while unattended. This is very useful if you have created multiple projects and don't want to babysit iDVD. You can istead leave it working on a queue of projects overnight, for example, and have a bunch of disk images waiting for you when you get back.
To do this, open Script Editor and paste in the following AppleScript.
tell application "iDVD"
with timeout of (24 * 60 * 60) seconds -- 1 day
-- Repeat the following two lines for each project you want rendered.
-- Be sure each project is rendered to a different image file.
open project path "/Users/michael/Movies/Spiffy Project.dvdproj"
start disc image burn path "/Users/michael/Movies/Spiffy DVD Image.img"
end timeout
end tell
Edit the open project and start disc image burn lines as appropriate for your iDVD project. Make copies of those two lines for each project you want to render. When you're done, hit Run to start the script.
Mac OS X Hints
http://hints.macworld.com/article.php?story=200809060044315