Here's how top get a slideshow that will let the viewer manually control the forward and backward movement of the slides with the forward and back buttons on the DVD remote.
1 - put the images you want to use in an iPhoto album.
2 - launch iDVD, select a theme and add a slideshow using the "+" button at the bottom:
3 - click on the Media button at the lower right hand corner of the window and then click on the Photos button.
4 - locate the iPhoto album containing your photos and drag it into the left hand pane:
5 - select Side Duration to Manual.
In order to get the maximum manual control of the slides you cannot have add any music to the slideshow. If you do add music the slideshow will continue you advance unless you pause the slideshow and/or use the advance/back buttons and then pause.
Once you have the project as you want it save it as a disk image via the File ➙ Save as Disk Image menu option. This will separate the encoding process from the burn process.
To check the encoding mount the disk image and launch DVD Player and play it. If it plays OK with DVD Player the encoding was good.
Then burn to disk with Disk Utility or Toast at the slowest speed available (2x-4x) to assure the best burn quality. Always use top quality media: Verbatim, Maxell or Taiyo Yuden DVD-R are the most recommended in these forums.