Here is a neat little screencast that shows you how to run the Microsoft Assessment and Planning toolkit, which we refer to as “MAPS” because we use it with our SQL Server customers to discover SQL Server instances, databases, servers, etc. It is a tool that Microsoft solutions teams build and maintain and it is free. There are links to download it from the screenscast URL at the beginning of this message.
The MAP tool provides assessment and planning information in the form of reports as output that you can use for Windows desktop, server, SQL Server and other Microsoft tools. But if you just want to get a network scan and SQL Server instance count to inventory what SQL Servers you have running out there, this is a great free tool.
It is agent-less and requires access via WMI to machines on a list that you create or on a subnet. The output reports show you the SQL Server version, edition and information about the server that it is running on. Examples of the reports are in the link that I included in this post.