Microsoft Assessment and Planning (MAP) Toolkit

The Microsoft Assessment and Planning (MAP) Toolkit is a powerful inventory, assessment and reporting tool that can securely assess IT environments for various platform migrations and virtualization without the use of any software agents.

http://technet.microsoft.com/en-us/solutionaccelerators/dd537566.aspx

And

http://technet.microsoft.com/en-us/library/bb977556.aspx