You're on the right track.
Use File > Make Movie
If you are using PowerPoint 2008 you can import the movie file directly
into iDVD and burn the DVD.
If you are using PowerPoint 2004 you first have to open the saved file
in QuickTime Pro, then use File > Export and export the movie as a
QuickTime movie. I know that sounds stupid, given that it's a QuickTime
movie in the first place, but iDVD won't recognize a QuickTime movie
saved by PowerPoint 2004. It's a bug of PowerPoint 2004 that was never
MVPs are independent experts who are not affiliated with Microsoft.