If you can't wait for November 11th when Call of Duty launches with its Zombie Survival Mode, and you REALLY can't wait until November 18th when Left 4 Dead launches with it's 4 player co-op campaign - then there is a solution. Right now pre-ordering Left 4 Dead through Gamestop will yield you early access to the demo.
According to a note on the Gamestop website your early access is valid from 11/6 through 11/11. We are presuming that the demo is launching to the rest of the non believers on the 11th then. This offer applies to both the Xbox 360 and PC versions of the game.
In other Left 4 Dead news, BigDownload is reporting that the hardware requirements for the PC version have been loosened up a bit. The video memory requirements have been dropped from 256MB to 128MB. This should allow more players to join in on the zombie massacre.