I've recently been creating some DVDs of pictures for some friends. I found a few things that others might fin helpful.
First, use iPhoto to create the slideshow and then share it to iDVD, rather than creating the slideshow in iDVD itself. There are more bells and whistles in iPhoto and the results are better. This isn't hard, once you have a collection of photos, just click on the "slideshow" button at the bottom, play with the settings, and then export it to iDVD. Exporting takes a long time.
Once it's in iDVD, you can choose a theme, edit text on the titles, choose a menu picture and audio, and you're ready to burn. I found this article at Mac DevCenter that talks about how to use iPhoto's greeting card feature to create slideshow titles, if you're looking for something fancy.