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
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.