MCE is basically just a skin for windows media player. Its a little bit more involved than that but that's the basics. Plug ins can be written for it but I have never seen any of them come close to being able to do GPS or OBD. Its a home entertainment system pure plain and simple. The Vista version is also far too buggy at the mo for a car environment as well, particularly on the standby hibernate area. Plus you have to hack it to get it to do something simple like play XVID or DIVX video.
Why would you want to use RR which is a front end to operate another front end?