I've just finished installing Mapguide 6.5 SP1 on Windows 2008 server and IIS7. The process may not be for the feint of heart. It involved a bit of hackery like modifying the windows installer package to remove the MDAC pre-requisite as well as a little fun getting the ISAPI working on IIS 7. I've documented the process on my blog thing.
hopefully this comes in handy for someone, sorry I was a couple of years late