BitLocker Drive Encryption is a full disk encryption feature included with the Ultimate and Enterprise editions of Microsoft's Windows Vista and Windows 7 desktop operating systems, as well as the Windows Server 2008 and Windows Server 2008 R2 server platforms. It is designed to protect data by providing encryption for entire volumes. By default it uses the AES encryption algorithm in CBC mode with a 128 bit key, combined with the Elephant diffuser for additional disk encryption specific security not provided by AES.
BitLocker is available only in the Enterprise and Ultimate editions of Windows Vista and Windows 7. Users of other versions of Windows that don't include BitLocker could use a 3rd party encryption program to satisfy the need for full drive encryption
This video tutorial shows a demonstration of Bitlocker