Visual Problems in iDVD

I've been using iDVD to burn home movies for the past three years. For the first two years its worked great, but for the last year I've been having this problem:
I can import iMovie/Quicktime movies into iDVD. But when I choose a theme, instead of getting a background, all I get is black. I can still see whatever title I've typed in and the button to click to play the movie. When I play it, I can hear audio/music if it's there, and I can use the menus. The drop zones don't work, either.
I started out with some 5.-something version, but upgraded to iLife '08 & that version (7.0) a few weeks ago. Same problem.
Someone suggested that I go into the Prefs, to where it said 'look in this folder for themes' and remove & re-enter the theme folder. But iDVD won't let me delete the original folder.
Any ideas? Please help me!

you might try draging that folder to your desktop and reinstalling '08. Another test is create a test user account (administrative) and try to make it in that user. If it works like it should you have narrowed down the problem to the other account.