Consult the ARP table. Then you'll get the MAC address, this you can match with the vendor via:
http://www.adminsub.net/mac-address-finder
command:
arp -a
use the following command to see the name of the computer:
nbtstat –a <ipaddress>
if you are lucky, you can also gather information via scans (ex program: autoscan, nmap, ...)