Microsoft released an updated version of the release notes for Exchange 2007 Beta 2. They're dated August 3.
Among the changes and clarifications, they've explicitly addressed the whole "which version of Monad/Powershell do I use" issue. I also don't remember seeing this the first time around:
Command line Setup changes If you run Setup from a command prompt, and if you are installing the first Exchange server in the organization, you must include the /OrganizationName parameter to specify the name of your Exchange organization. This is a required parameter, and Setup will fail if it is not included.