I've been unable to find any documentation of how to use the built-in IR blasters. I suspect this is one of the "undocumented" Microsoft API.
I have a somewhat inside source @ Phillips, I'll see if I can find anything on it. Though since it appears it is made specifically (and only) for Windows/MCE it may be unattainable.
Do you know if I were to get one of the supported IR Blasters if the MCE remote would work with it (I would assume so since the IR blaster selection is independent from the remote selection in your application)?