The easiest way is to create a QuickTime Movie from your PowerPoint file
(File -> Make Movie). If it looks like how you want it to, drag it into
iDVD to convert it. You can then make adjustments to the DVD settings in
iDVD and burn the disc.
The other way is to use an application like Snapz Pro
<
http://www.ambrosiasw.com/utilities/> and record the entire screen during
your presentation as a QuickTime Movie. It's a little more tedious, but it
will save your movie exactly as it appears in PowerPoint. You can then drag
the resulting file into iDVD to insert it, and then burn the disc.