There isn't an easy solution, but there are two options.
1. If you have access to the Domain Controller, you can query it's client
list. This will only give you computers in the domain, not routers or
switches, or other non-domain machines.
2. Use SNMP to query the Router that routes packets on your LAN for it's ARP
table.
Or, query the DHCP server to find out the scope. But, probably the
simplest, and slowest, is just to find out your IP and ping each IP on your
subnet. this fails if you have multiple networks.