Hi there,
You could do a slideshow in iPhoto and import into iMovie, but I'd recommend using iMovie for everything -- import the stills and video clips into iMovie; organize the sequences; add the background audio; and test it. If it looks fine, import to iDVD for burning the whole production to DVD.
iMovie can export to various video formats, but can't instruct your computer to burn videos to disk. iDVD lets you create menus (like on a commercial DVD) and encodes videos into the correct format/codec (mpeg-2 video) for playback on standard DVD players, and burns everything onto a DVD. Apple's software is integrated, so it can seem a little blurry between iDVD and iMovie and iPhoto.
John