Enemy Within will take place in a different world and timeline than the Half-Life games and there is going to be heavy emphasis on storytelling.
The first episode is set to be released before Christmas 2007.
More information at www.enemy-within.com
At the moment EW is being developed by a single person.
The mod is in need of a programmer to solve a few minor tasks. For more information see http://www.enemy-within.com/help.html