Specifications for BF Bad Company 2 for PC and BF1943

Minimum Frostbite PC Specifications for BFBC2 & BF1943
Processor: Core 2 Duo @ 2.0GHz
Main memory: 2GB
Graphics card: GeForce 7800 GT  / ATI X1900
Graphics memory: 256MB
OS: Windows XP
Free HDD space: 15GB for Digital Version, 10GB for Disc Version (BFBC2)
                                 10GB for Digital Version (BF1943)

 
Recommended Frostbite PC Specifications for BFBC2 & BF1943
Processor: Quadcore
Main memory: 2GB
Graphics card: GeForce GTX 260/ ATI Radeon 4870
Graphics memory: 512MB
OS: Windows Vista or Windows 7
Free HDD space: 15GB for Digital Version, 10GB for Disc Version (BFBC2) 10GB for Digital Version (BF1943) 

One thing the specifications don't say is, in order to do DirectX 11, you need Vista SP2 or Windows 7 and a 5000 series ATI card (or a GTX470/80 when they come out).

This game is great in DirectX 11 and if you have the proper hardware/OS it will automatically detect what you have and load the proper level of code.

More info from the developers