I'm gearing up for Left 4 Dead II
demo coming out on October 27th on the PC and here are the details from Gamer's Digest
. You'll be able to play through some of The Parish campaign that was playable at E3. What you do get over that demo though is all the new Special Infected zombies will be on hand to piss you off and all the weapons will also be accessible.
Now, only those that pre-order get the demo on October 27th. If you're an Xbox Live Gold member, you get it on November 3rd as well as the rest of the PC folks. Finally, the rest of the Xbox Live members can have at it on November 10th.