If everything goes OK Exchange 2007 Service Pack 2 will be released tonight and else tomorrow. That’s what a post from Paul Rowden (Release Manager Exchange Development) will tell you. Paul posted the text below:
Additionally, Exchange 2007 SP2, which releases tomorrow will also contain the same AD schema extensions as Exchange 2010.
So now it’s just waiting for the links to be available but it won’t take long I think. Now SP2 will be released it’s officially supported to have Exchange 2010 RC can run in the same organization as Exchange 2007. One of the pre-requisits is that you need Exchange 2007 SP2. The SP will contain new schema extensions which are also used with Exchange 2010 RC.