Lo and behold, as fate would have it, the iDVD project has vanished (or in my case, was eaten by a recent HDD failure). Luckily for you, savvy OS X user, there's still a way to get a copy of that holiday montage onto a disc for Grandma to use.
Over at MacFixIt, there is a pretty simple tutorial for making a backup or copy of an unprotected DVD. In the past, TUAW has covered some methods of using downloaded software to back up DVDs that you don't own. The MacFixIt tutorial provides handy information about how to copy unprotected DVDs that you do own, using the software that is baked right into OS X.
The basic process involves inserting the DVD, firing up Disk Utility, and making an image file using the DVD as a source. From there you can either retain the image file for future use/backing up or you can burn it to disc and pass it off to any friend/relative of your choosing.
This method will work for any unencrypted DVD, not just iDVDs made on a Mac. That means you can work with discs created by your Windows-loving cousin who swears that Windows 7 is not going to have any of the problems that Windows Vista had.