If you can't reset the print server to factory default then you could
have a long job here if you haven't used the print servers recently.

Bit of background; the way two peices of kit on an IP network
communicate at low level is using the MAC address, when you access
something using it's IP address PC's, switches and routers have to get
the MAC address for that device by what is termed ARPing for it. The
PC and routers then store this information for each device they have
communicated with recently in what is known as an ARP table. Typing
ARP -a displays the contents of this table.

So what you have to do is to get the entries for these devices into the
ARP table and the only way I can see of doing this is to ping every
device on the sub net and then go looking in the ARP table for the MAC
addresses you already know.

There is a ping sweep application that does one better and provides the
IP versus MAC for you available free at

http://www.insecure.org/nmap/nmap_download.html

Which will make pinging a large network easier, I just tried it and it
works.

When you have loaded it (and the WinPcap library it tells you about)
you just type:

nmap.exe -sP 172.101.100.* return

but replace the 172.101.100.* with your network address range and you
will be rewarded with a screen full of IP / MAC addresses.

Load the output into a text editor and search for the MAC address you
want.