You can now download the Perfect Dark Zero demo from the Xbox Live Marketplace. This demo will allow single player or co-op play.
Mutliplayer over Xbox Live is not part of this demo. This free demo is available in all Xbox Live regions.
Edit: fixed a typo.
Edit: I was wrong…the demo DOES allow Xbox Live Play.
Here is what is in this demo, directly from the PDZ Team:
Outpost, the story mode level included in the Demo, is playable co-op over Live.
Plaza (a new map included in the upcoming DLC) is playable over Live in Team Killcount and Infection game types. (Bots are included in both game modes.) The disabled Live features are Leaderboards and Custom Match. Quick Match works for both game types