Information is scarce right now, but the sum total seems to be this: It'll be released for the XBox Live Arcade, instead of as a boxed game. I think it's assumed the game will also come out via Steam, but I don't think there's any super-official confirmation of that.
This second title, called "Portal: Still Alive" (Try Googling that to get some information. Is good time, yes?) will be a "continuation" of the original game, and include a "new challenge mode".
As Kotaku astutely notes, we were told in April 2008 that we "won't see a new Portal this year". Since this new game is slated for release in 2008, it seems there have been some crossed signals.


yeah but seriously. we got good stuff. atleast 2 good portal map packs. and MANY good individual maps. plus our community map project that may see light someday. regardless. UNLESS this is just like a map pack that valve put together, or peiced together from user maps. i seriously doubt it would be xbox only. but if it is just new maps without alot of new concept then they might, cuz they know that we (the pc users) would unlikely pay $19.99 (usual single game price) just to get maps. when we got ALOT here online. if there is more to it than that, i have no doubt they will release it on pc too i mean if nothing else. a steam release doesn't cost them much in the way of advertising, production, etc. since most of that will already have been done via the xbox release.
but.. then we would need a Chell npc in ep3 