Flip me on my side, cover me in marmite and call me Tarquin! It works!
The drive in my Intel iMac is now Region Free
Here's what I did:
Applied the patch under Tiger (10.4.11)
Rebooted into 10.5.1
Deleted the following items:
~/Library/Application Support/DVD Player.
~/Library/Preferences/com.apple.DVDPlayer.plist
I then ran Region X, set the region to Region 2 and quit Region X.
I then launched DVD Player and inserted "The Day Of The Triffids" (BBC Series, pure class). DVD Player was more than happy with it and played the disk.
I quit DVD Player, launched Region X, switch to Region 1, quit Region X, relaunched DVD Player and inserted "Bad Santa - Directors Cut". Again DVD Player was happy to play the DVD, no dialog asking about region switching
I tried switching back and forth like that a few times and it's still working