A new Drizzle version over clean unplayed copies of Uru CC, MOUL folder and the Myst 5 game.
As I said, the CC does not *have* to be clean or unplayed. It is certainly possible to continue using the old installation and just install/convert new version on top of the old ones, which I actually did during at least 1.5 years of Offline KI development. Ok, I had to reset my avatar some times because I screwed it up, but that was due to bugs in the code, a release version should never do that. The avatar I reset it to is still the original one I created back in 2007 when I first played the game, btw
That said, if you run into problems by just upgrading, it might be a good idea to start from scratch. As this is a whole lot of work though, it should not be required. It's also good to hear that if you beta-test a KI I send you, I can be sure you have no leftovers in your installation