Best and easiest way (not cheapest) is to buy the MCE remote - or a Hauppauge MCE card w/remote bundle. Reciever will work with Harmony.
I'm wondering about harmony remotes as well. What I want is to be able to press one button that not only turns on the television set, but also cranks up MediaPortal's TV full-screen. Does anyone have any experience in trying to set up macros like this using a Harmony remote?