The themes are part of the iDVD2 Application 'package'. If you right click on the app and choose show contents, then you'll be able to dig into the applcation and see that it's actually made of loads of files and resources.
DO NOT CHANGE A THING, and afterwards, right click on the original file and choose hide contents. iDVD2 is 750MB big or there abouts. All of the themes are written into the Apps services. It's unlikely that anyone except Apple will make more thems. But come on it's really easy to make themes.
I just wish that not all buttons within th same screen/folder have to have the same buton theme. ie the Slide show has one theme and the movie themes a different. And I'd love to be able to make your own themed buttons. I'm sure you can , by ripping the contents apart od PhotoShoping some files. But I wouldn't risk it.
I've realised through experiments that iDVD only likes .mov files. Also you have to keep to the right TV standard. PAL/NTSC/SECAM and so on. So if your messing about with an American (NTSC) project, you can't import British PAL files. Unless you have change them with QuickTime Pro. (worth it's money in Gold). I've managed to use different codecs but keep the file a .mov to a moderate amount of sucess. So if you want to use a divX file, convert it first with QTime then al lwill be well.
iDVD 2 also allows .aiff and .mp3 files for music and sound. And .jpg and .tif files for pictures. Some times a particular file won't work. Again just use QT (for sounds and video) or Graphic Convertor to REsave it and all should be well.
60 minutes is the maximum at the higher bit rate (higher quality picture) but if you go over, iDVD will automatically change the bit rate and give you a new maximum. 90 minutes which IS the most allowed.
This is because iDVD is intended to be used only with the SuperDrive which can only record the smallest DVDs possible (12cm).
DVD Studio Pro can use all of the differnt DVD's used as long as you export to a DLT tape and give it to a media house.
DVD4
DVD9
DVD18
there are a few more, but basically you can use
Single Sided - Mono Layer 4.7GB
Single Sided - Dual Layer 9GB
Double Sided - Mono Layer 8.4GB
Double Sided - Dual Layer 18GB
So you can make an 18GB project but it means that your SuperDrive (if you have one) is useless. You'd have to export to a DLT tape. You could theoretically use a Mono Layer double sided. But I haven't seen a consumer available product yet.
Hope that helps
Could you download more themes for iDVD2 from any sites?