export menus possible?
 

Is it possible to export motion menus from idvd to be used with encore cs3? Or even pull a motion menu off of any finished dvd and use it in another authoring program?

Unfortunately iDVD and Encore do not use the same abstraction-layer programming language to create their user interface or working tool structure, much like you can't load a Windows ".exe" file and run it in OSX.

With regard to pulling a motion menu it is possible using MPEGStreamclip to demux the menus (to what degree I have not tested) however what you'll have is the highly-compressed MPEG2 version of the movie that was used, not the original file it was created from. Be sure you're the content owner (or control the rights to it) before ripping apart any DVD to avoid copyright infringement.

You can access the individual quicktime and tif elements of the themes if you go into your Macintosh HD/Library/Application Support/iDVD/Themes and then "Show Package Contents" of any theme you like. If you open the contents/resources you will then see all of the individual elements that can be rebuilt in DVD Studio Pro or possibly other authoring apps.