Dan Kershaw has produced (and updated) a whitepaper for folks who don't want their TFS AppTier and SharePoint servers on the same machine.

Unfortunately, the doc seems to have moved since most of the links out there were created. As of right now, it's located here: http://msdn2.microsoft.com/en-us/teamsystem/aa718901.aspx

Warning: I'll quote Brian's post on the original link - this process is NOT simple: "The instructions are neither simp