If you need to get the MAC address of a device you can use Nmap.
Use the following command:
nmap -sP -n 192.168.X.X
You will get an output that looks like this:
Starting Nmap 4.62 ( http://nmap.org ) at 2012-06-15 15:12 BST Host 10.1.1.3 appears to be up. MAC Address: 00:90:7F:1C:8B:EE (WatchGuard Technologies) Nmap done: 1 IP address (1 host up) scanned in 0.111 seconds