Gee Gee
I'm no expert on either iMovie or iDVD (and this is the iPhoto forum) but here's a way of doing it:
Create your Slide show in PhotoToMovie (
http://http://lqgraphics.com/software/phototomovie.php)
This is a slideshow software with much more control and potential than iPhoto. Then export it to a Quicktime Movie.
A more traditional slideshow app is PhotoPresenter:
http://www.arizona-software.ch/applications/photopresenter/en/
It also exports to Quicktime.
Then, with iMovie or QuickTime Pro, splice the Slideshow and the Movie together.
IF you want the Video in the middle, then obviously make the slideshow in two parts.