Developer DICE has released some information about Battlefield: Bad Company 2:
In the Vietnam-extension players get 4 new multipayermaps (all located in Vietnam, where else

), 15 new weapons and 6 new vehicles.
The gameplay has been changed: the players will be now be able to take cover in foxholes, tunnels and/or in the dense jungle.
And all the gameplaymodi from the original will be available in this extension and you will be able to continue to level up your soldier as usual.
To create a specific atmosphere DICE has recorded special voice-overs (for both sides), based on authentic dialogue from the Vietnam war. The extension gets also an own soundtrack with about 2 hours of music from the sixties.