Hi -- I have had the same problem and it drove me nuts. I've tried repairing the permissions and the disk itself, but the Disk Utility would give me an "Illegal Name" error. After further investigation I ran across this thread on the Adobe forum...
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http://www.adobe.com/support/techdocs/332657.html
Long story short, my built in iSight on my MBP15 is working fin again! Here is what I did:
1. Followed the instructions in the above mentioned thread (Remove "Legal" dirs from Adobe CS2)
2. Boot from Installer Disk/CD
3. Launch Disk Utility
4. Repair Disk & Repair Permissions
5. Restart back into OSX
Hope this helps others running into the same problem.
Good Luck!
Kai
MacBook Pro15 Mac OS X (10.4.6)