PowerShell get a list of network machines

Soemtimes the old school way is the easiest.

net view

Here's another thing you can do (depending on your worgroup name).

([adsi]"WinNT://WORKGROUP").Children

Piggy-backing on Shay's answer:

([adsi]"WinNT://$((Get-WMIObject Win32_ComputerSystem).Domain)").Children

This will grab your domain or workgroup name and use that for you.