Click Start->Run type cmd and click enter (start command line prompt). Now depending on version of installed sql server client tools run either from the following commands
sqlcmd -L
osql -L
isql -L
Try them in the given order. sqlcmd is the latest version of command line sql server utility. All of this utilities support -L parameter which lists all sql server instances from the network. However, isql shows only sql servers of 7.0 version and below, osql - only sql server 2000 and below and sqlcmd shows all sql server instances from the network. So to view all sql server in the network you better use sqlcmd -L command.
