Ian,
I had this issue come up with a major customer. Windows 2000 / 2003 does not
offer a built in out of the box way to do this. This will need to be scripted
one way or another. If you are auditing for account logon events, you can
parse the security logs on DCs (useful tool is Event Comb) and go based on
the information in the events.
There are scripts that search where the user has logged on, but most that I
have seen require that computer browser / WINS is configured.
There is a psLoggedOn utility on sysinternals and I talked to a person who
uses a third party utility by Hammer Software called MetaLan
http://www.hammer-software.com/index.php?page_id=19
I fought with this for three weeks. Not that easy. If you find another way
let me know.