i thought i'd let people in on this, its a sneek preview of the upcoming free DLC for l4d, and one of the modes is this, Survival Mode. Suffice to say the g4tv team is sucky at it, but atleast you can see one of the new levels exclusively to this mode.

http://g4tv.com/thefeed/blog/post/694858/Left-4-Dead-Survival-ModeDLC-Preview.html