Well I have uninstalled Windows 7 and gone back to Windows XP MCE 2005.
There were too many problems with it from the lack of response to the remote control, the frequent and unidentifiable pauses while browsing menus in Mediaportal and my inability to get DXVA working.
The developers blog notes that MP isn’t supported on Win7 and now I can see why. Give it a few months and I am sure they will have it working smoothly – probably with 1.1RCx which is a long while overdue (the reason?).