Active Directory User add to Linux Group

[KJS]

Hi Guys,

Let me explain my setup... We have a 2003 SBS box and a Samba server, 
the 2003 Server does the Active Directory authentication for the Linux 
box, which is working fine for samba and local auth and SSH.

However, I need to add a user from Active Directory (a virtual user 
really), to a local group. Now this does not seem to be easy, I can't 
just usermod the Active Directory user to add a group as I get "User not 
found in /etc/passwd" or similar error.

Having poked around on Google I have found that most people are saying 
you need to do this from the Active Directory server, but how is the AD 
server going to be aware of the Groups on my Linux server??

Thanks In Advance!

KJS