As a follow-up to the initial Killzone 2 DLC announcement, the details have now been revealed as follows:
It's a http://www.gametrailers.com/player/47376.html entitled Steel & Titanium. There will be two new maps in the pack; the first will be on the ISA flagship the New Sun (vertical play), and a map featuring 2 Helghan trains running right next to each other with environmental gotchas if you're in the wrong place at the wrong time.
Both are obviously ripped out of the single player missions; nevertheless, they sound fun.
Time-frame is end of April; no price announced but that doesn't mean it's free...
Oh yes, Guerrilla is working on map pack 2 already and the word to think about is "Retro."