Exchange 2000

Here we go….. I have a NT/2000 environment. Exchange 5.5 on an NT box. Want to upgrade to Exchange 2000. It appears this must run on W2K. Also that you must have AD setup and running. Stop me if I am wrong here. What is my best course of action to do this at this point? Build a new server with W2k then install 5.5 and then upgrade to Exchange 2000? Can AD be running on some other W2k server currently installed?