Adding Trusted NT Domain users

We have recently merged with a company who is still running an NT
domain (upgrade to our AD planned for Jan).

In the meantime we need them to start accessing documents within SPS
2003.

Now I have them all as contacts with the Exchange Alias and AD
Description as DOMAIN_NT\user

What I would like is when I add the user user@xxxxxxxxxx it would then
population the User Name field with the Alias (All the local AD aliases
are the user names), would this be possible?

The reason is there is no standard format for the remote users, and I
do not want a few hundred people here guessing a few hundred names
there. And putting out a sprea*** with the details on it.

Many thanks in advance

.