The way I read the question is a little different; basically, there isn't a search facility in the console that lets you
find a client based on the MAC address. Because of that, what "bnixon" is asking for is unreasonably difficult to do.
However, it's a reasonable thing to want to do. Since I posted a script that reads from the console database in answer to a forum post just yesterday, I thought I could adapt that script to create a printable version of the MAC addresses each machine has (the raw data in the database being a binary encoding that's hard to search directly).
So, I did that and then added a simple string search on top of that, and having found a match it then prints the names of the matching machines so you can find them in the console. The script only looks inside the "Default" folder, but hopefully it might be useful for this; it's available
here. Double-click on the WSF file in the archive and you should be prompted to enter a search pattern, which can be any fragment of a MAC address with the elements separated by hyphens, e.g. 00-15-C5
Let me know if the script doesn't work for you, it's just something I whipped up at home so I haven't tested on anything other than a Windows XP machine. The script just lets you find the machine you want, but from that it's easy to assign it as the target of a task.
By the way, a useful resource for working with MAC addresses is the IEEE's
OUI Registry which lets you find the manufacturer to which a MAC address is assigned (the first 3 bytes of every MAC address being the OUI part which identifies the manufacturer). For instance, my example 00-15-C5 is assigned to Dell.