I'd advise anyone who installed the 2.2 leak to wait until 928Droid advises that it is ok to install his theme with this leak. As you can see from the original post, the theme was last updated on 8/15/2010, so it may only be compatible with 2.1. I am not sure if the framework and service.jar would be different to theme, but you never know.
I will wait for the man himself to give us a heads up if it is good to install or not.
Thats the best option anytime, wait for instructions. That being said, I'm 99.9% sure that installing this theme over 2.2 is going to cause serious problems. Certain files and images are located in different places with 2.2 and the theme wont know about that, so things are going to be put in the wrong places.
Give it a little time, 928 will have it up and running for the X with Froyo soon.