Courtesy of Comcast, the map, entitled "Comcast Event", conjures up thoughts of cheap cabling, rude customer service, and a broken On-Demand service...One can only hope this map involves none of those things. No word on what exactly this map is or what it contains, but if you are interested here are the instructions, which are also viewable here:
1) Go to the Main Menu of Rainbow 6: Vegas 2.
2) Select Extras.
3) Select Comcast Gift.
4) Enter the code Comcast Faster when prompted and enjoy the new multi-player map, Comcast Event, the next time you play.
No matter where this map is from, I can't help but feel happy that there is some downloadable content for a game the day it is released!