Jak, glad to hear you were able to (mostly) get the 2 DVD method to work. I'm not sure what's giving you the issue with the game playing that last video. When I did it, I believe it just skipped it, much like it did with other files that were in the Mainvideo file. I'm not 100% certain, though. I haven't played my backup in a while.
If you wanted to get crazy, you could create yet another disc with the maindata and mainvideo files, then cut out all the other episode except the last 2 or 3. That would keep all the end credit videos on the same disc, and you'd be able to save the game following completion of episode 20. But, then again, that's making
another game disc, and I don't think that's the result you want.
I'll check out my discs to see if I did anything special to make that work. Don't think so.
Anyway, good luck, and glad it worked so far.
-!SB!-