Here'a a couple of what sounds like a decent tool I found in 10 minutes using my assistant DBA, Google. 😛
I like this first one the most because I can call Powershell from xp_CmdShell (captures the result set directly) or just run Powershell separately and pipe the output to an importable file.
Here's another that goes above and beyond.
http://www.straightpathsql.com/archives/2009/02/what-sql-instances-are-installed-on-my-network/
http://www.microsoft.com/en-us/download/details.aspx?id=7826
MAP (Microsoft Assessment and Planning Toolkit) (from the links above) supposedly makes a spreadsheet and a word document with all the goodies you might care to lookup.
--Jeff Moden
Change is inevitable... Change for the better is not.