You're at a computer, and want to see what other computers are on the network, but don't have a scanner. What do you do? Try this simple command line code inside cmd.exe:

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

c:\>for /l %a in (1,1,254) do @cls & @Echo Pinging 192.168.40.%a... & @Type Ping
Results.txt & @Ping 192.168.40.%a -n 1 -w 50 | find "TTL" >> PingResults.txt

  It's not pretty, but once you figure out how it works, it's easy to type on site, and finds you all hosts that reply to ICMP. Just change the 192.168.40 to match your current subnet.