From www.rainbowsixgame.com:

The Rainbow Six Lockdown PC Demo is OUT! Get it now. A great way to find others playing the demo is to download Xfire and add the alias rainbowsixgame.

Quick Demo Notes

* R6LD PC final demo will be both Single player and Multiplayer.
* The MP map is Prison and the ONLY game mode available is ‘Team Adversarial’ aka team deathmatch
* The SP map is Mission 1 South Africa and you can only play ‘Campaign Mission’ on it. You can play this mission on two different difficulty modes: ‘Normal’ and ‘Challenge’
* The minimum specs are the same as for the final game. System requirements attached.
* There are 17 weapons available (42 in the final game)
* All the equipment and grenades are available for both SP and MP
* Custom Character creation and usage available for MP
* The size of the demo is 450 Mo.

Mirrors

* 3DGamers
* WorthPlaying
* FileShack
* Gamer’s Hell
* Games Planet
* Clubic
* Filefront

Hopefully this will be a great addition to the franchise! I encourage you to check it out!