First drag and drop the icon for iDvd on the dock to the desktop. It should vanish in a "puff".
Now go to your applications folder on the boot volume (your main HD) and launch iDvd directly from there with a double click on the iDvd folder. Does the app launch as expected, or not?
If not, drag and drop the plist for iDvd to the trash and Restart your mac. Use the finder (happy face on the dock) to locate this item/s:
com.apple.iDvd.plist
Try the app again directly from the applications folder. Let's assume it now launches as expected. Now drag the app for iDvd directly to your dock and you will now be able to launch iDvd from the dock.
If neither of the above are of any help then you may also need to perform these steps as well:
http://support.apple.com/kb/TS1972
Good luck.
Message was edited by: SDMacuser