The teaser — due on February 15th / 16th (North America / Europe) — will drop players mid-way into the single-player campaign, allowing them to explore the Icy Incursion stage. There'll be two versions of the demo available — 2D and 3D. There's not a huge difference between the two (aside from the obvious), though the 2D demo will be the only one to support local co-op. Both demos will support the PlayStation Move.
PlayStation Plus subscribers will be able to get in on the action a week earlier, as the demo will be available a week on February 9th to subscribers.
Killzone 3 is also getting an open multiplayer beta at the start of February. Click here for more details on that.