My first bit of troubleshooting advice is to make sure you’re running the latest versions of iMovie and iDVD; check the iLife page at Apple’s Web site (www.apple.com/ilife/) or run Software Update (in your System Preferences or from the Apple menu).
Also, check Apple’s online support discussion forums for iMovie and iDVD (discussions. info.apple.com) to see if other users have found solutions or workarounds to a problem you may be experiencing. I owe a great debt to many folks online who have prodded the programs to find answers.
Finally—and perhaps most important—give Apple feedback (www.apple.com/feedback). It’s the best way to communicate what needs fixing (and yes, the developers do listen).