Unfortunately, no. iDVD was discontinued, and can not be downloaded.
iDVD can still be found on the iLife 09 DVD discs, and the early releases of the iLife 11 DVD discs. You should be able to find a copy of these DVD's on eBay or Amazon.
I would purchase a copy of iLife 09 over the iLife 11 DVD disc, if you can, as I understand it has more available themes, then the version on iLife 11 DVD disc's.
If you plan on purchasing an iLife disc remember that the iLife 11 disc only provides iDVD 5-7 themes. The Software Update no longer installs the earlier themes nor do any of the iDVD 7 updaters available from the Apple Downloads website contain them.
Currently the only sure fire way to get all themes is to start with the iLife 09 disc:
This shows the iDVD contents in the iLife 09 disc via Pacifist:
You then can upgrade from iDVD 7.0.3 to iDVD 7.1.2 via the updaters at the Apple Downloads webpage.