MAPT 3.2 tool.   It is a non-invasive tool that will probe AD for all Windows Servers and SQL Server information.    This can help qualify your base SQL footprint for you.

Link to the MAPT 3.2 Tool:

http://www.microsoft.com/downloads/details.aspx?FamilyID=67240b76-3148-4e49-943d-4d9ea7f77730&displaylang=en