Full screen TV from iDVD?

I moved from PC to Mac 3 weeks ago and ever since I've tried unsuccessfully with iDVD6 to burn a DVD slideshow which shows full screen on my non-HD TV. No matter what I fiddle with, the DVD photos show in the middle of the TV screen totally surrounded with black. Previously I used EZDVDCreator on the PC and made full screen slideshows on the same TV, so I know it is not a TV issue.
I do not export the photos from iPhoto. I merely begin with iDVD and find the pics in iPhoto.
What do you suppose I'm doing wrong, or failing to do?
Thakns a lot

are the themes set into 3:4?
not 9:16 which is standard in idvd

Well I thought I had 4:3 because that's the TV, but I was wrong. So I'm making the change and reburning, which takes quite a while I've found-even with only several slides as a test.
Thanks a lot. I'll report back.

Make sure the pictures are the correct resolution. If they are lower resolution they will not fill the whole screen.

Bingo!
I think the 4:3 change did it.
Thank you very much.
jim