samba - Nov 2002 - Dot in username - clients cannot auth to Win2k AD servers

We have an Active Directory with about 2000 users in it.  Usernames are in the 
form firstname.lastname
When trying to mount a share with a username creating a dot, I get ERRDOS, 
even when I'm positive that I have the right password.  I've tried
double-
and single-quoting the username, as well as escaping the dot thus: 
firstname\.lastname but nothing has worked.  I know I have rwx rights to the 
shares I'm trying to mount, but I can' t mount them from any Linux
machine.
By contrast, I can mount using OS X, so it's not a generic unix problem (I 
think).

Here's the mount command I've been using:
mount -t smbfs //server/share /mnt/smb -o username=user.name
which won't work, but
mount -t smbfs //server/share /mnt/smb -o username=username
works.

Thanks in advance for any help you might have.
Mike
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