At a command line:
SQLCMD -L
or
OSQL -L
(Note: must be a capital L)
This will list all the sql servers installed on your network. There are configuration options you can set to prevent a SQL Server from showing in the list. To do this…
At command line:
svrnetcn
In the enabled protocols list, select ‘TCP/IP’, then click properties. There is a check box for ‘Hide server’.