Heres a really simple way to start, enter this in a command line...
C:\Users\SevenStoryMountain>FOR /L %i IN (1,1,254) DO ping -n 1 192.168.1.%i | FIND /i "Reply">>ipaddresses.txt
this Script outputs ping results to ipaddresses.txt so you can easily see what IP addresses are being used on the network.
Make sure its run from a directory you have permissions to write to, otherwise specify a good path after the >>