Since iDVD has been discontinued by Apple the only way to obtain it is to purdchase an iLife 09 or 11 boxed version that is still available at the online Apple Store until supplies run out. If you have the boxed version it will be available to you for reinstallation any time it might be necessary to do so. The same goes with iWeb if you use it.
It is now apparent that iWeb, and iDVD, is no longer supported by Apple. This is evidenced by the fact that new Macs are shipping with iLife 11 installed but without iWeb and iDVD.
iWeb will still continue to work but without the following:
Features No Longer Available Once MobileMe is Discontinued:
◼ Password protection
◼ Blog and photo comments
◼ Blog search
◼ Hit counter
All of these issues can be solved with 3rd party options.
I found that if I published my site to a folder on my hard drive and then uploaded with a 3rd party FTP client subscriptions to slideshows and the RSS feed were broken. If I published directly from iWeb to the FPT server those two features continued to work correctly.
There's another problem and that's with iWeb's popup slideshows. Once the MMe servers are no longer online the popup slideshow buttons will not display their images.
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However, Roddy McKay and I have figured out a way to modify existing sites with those slideshows and iWeb itself so that those images will display as expected once MobileMe servers are gone. How to is described in this tutorial: #26 - How to Modify iWeb So Popup Slideshows Will Work After MobileMe is Discontinued.
It now appears that the iLife suite of applications offered on disc is now a discontinued product and the remaining supported iApps will only be available thru the App Store from now on. However, the boxed iLife 11 at the online Apple Store (Store button at the top of the page) and those still on the shelves of retailers will include iWeb and iDVD. Those two apps were listed in small, gray text on the iLife 11 box that I bought. Personally, if I already didn't have a copy I would purchase one to have it for reinstallation purposes if ever needed.
This might be of some interest to you at this time: Life After MobileMe.