Someone posted the following on a different forum a while back. I haven't tried it out, but it sounded useful, so i kept hold of it. Hopefully it'll work for you.
The Void
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Hi,
You can get iDVD from your install discs, without having to reinstall
everything - here's how to do it...
1: go to
http://www.versiontracker.com & download Tinkertool.
2: launch tinkertool. click on the finder tab & select the box 'show hidden
& system files' - restart the finder. This will allow you to see content on
your install CD that was unavailable before.
3: Double click on your install CD. iDVD will be in a (previously invisible
folder)called .images & will appear in the form of a disc image (dmg) - just
double click the folder image to open it..
4:Inside the disk image are 2 folders (applications & library).
5: In the applications folder is the iDVD application. Copy this to the
applications folder on your HD.
6: Open the library folder. Inside is another folder called 'receipts' &
inside the receipt folder is iDVD install receipt.Place this in your
receipts folder located in Computer HD/library/receipts.
Congratulations, you've just installed iDVD.
To put your finder back to normal simply relaunch Tinkertool - uncheck the
'show hidden & system files' box & restart your finder - Bobs a Job!
This method also works for itunes, Iphoto 7 any other bundled Apple iApps.
hope this helps