This is an old thread but as I was searching for some info came here and wanted to add some possibly helpful information. I too have a newish MBA with 10.8.5 (mountain lion) and an older MBP that had iDVD on it with ALL of the themes installed and working 1-7 (none greyed out). Needed iDVD on MBA and dragged the app from MBP to MBA and copied themes from library/application support/iDVD and came to the same problem as the others here. Themes from iDVD6 & 7 installed fine but the rest did not. The program works fine but with just those themes.
So after reading what EventSound did, installed from iLife 09 DVD - I dug around my install discs as I've been using macs and idvd etc for a long time. I found ilife 08 - (did not have ilife 09). I thought I'd try it and see.
Guess what - iLife '08 also has ALL of the idvd themes on it. So what I did was use an external drive to put the ilife 08 install dvd in and plugged it into my macbook air with mountain lion. (I did delete all iDVD themes and the program so I'd do a fresh install & repaired permissions) I selected 'custom install' of course and installed iDVD only - but selected the 'iDVD extra content' and checked that too. Now everything installed but on ilife 08 the version of idvd is 7.0 and cannot be opened in mountain lion but that's ok, as I said, it installed fine and then I updated idvd to idvd 7.0.4 (because I had already downloaded that updater from the apple website) and that was compatible with mountain lion and cool beans, I have ALL themes available in iDVD on my macbook air 10" with mountain lion 10.8.5.
Then I ran software update and updated to 7.1.2.
I also notice, Old Toad, that once I had already installed all the themes (1-5) - the old themes - THEN, software update/App store provides a link to download them. Still does that and it's now the end of October 2013.
So, to reiterate - ilife '08 install DVD (retail) has all the iDVD themes included as well. There is a simple work-around for mountain lion - just install one of the updates and you are good to go. It worked for me with MBA running 10.8.5