OK, I solved it for me, and perhaps you folks can use this information too.
It was a two step process.
Step 1. Go to your personal Library/Application Support/iDVD folder
Remove the Installed Themes folder
Step 2. Go to the system Library/Application Support/iDVD/Themes folder
Move the themes from the old versions of iDVD to some other place
I chose to move all of the themes from iDVD 1 thru iDVD 6 out of there.
Then start iDVD.
It looks like iDVD was crashing while it was trying to copy the themes from
the system iDVD/Themes folder into your personal iDVD/Installed Themes folder. Don't know why.
I also don't know that this will solve your problems too, but I'm hopeful.
Edit: After a little more research, it appears that iDVD 7 has problems only with iDVD 1 and iDVD 2 themes.
It still works after I put the themes from iDVD 3 thru iDVD 6 back into the system Library/Application Support/iDVD/Themes folder.