Media Center has zones that allow simultaneous playback of different playlists, but the feature was never intended for DJ use. There is no support for fading or cueing. Each zone is a perfectly independent entity. It's a design choice.
For DJ use a single playlist is required, and tracks have to be sent alternatively to different decks for playback. There are also other DJ features that MC does not cover, such as cue point, beat detection and so on...
I think that a real DJ software is more appropriate for DJ use. DJ software, however, entirely lack the organizational power MC has, and have no way of integrating with MC (even Replay Gain is not recognized by DJ software). The DJ software I tested is very obtrusive. It pretends to write its own tags (with its own name) into audio files, and there is no way to disable that. This screws up the MC library. The only way to prevent it from writing into files is to use a read-only share. This is not a reliable solution. Playback from the DJ software becomes very stuttering, unsuitable for live use.
So far I see little chance of integration between Media Center and DJ software. But I hope to be wrong, as I enjoy DJ software for playback as much as Media Center for organization.