[Samba] directory permissions

[Aubrey King]

I have just finished replacing a client's Windows / Exchange / IIS setup 
here with Samba / [Postfix, UW Imap] / Apache and I've run into an issue.  
In this setup, Samba acts as PDC, so there are NO WINDOWS SERVERS - only 
win clients.  One of the apps that they run seems to explicitly require 
that the user own the folder that they are saving to.  In their prior 
setup, this was easy, as you could set the directory owner to the users 
group in the domain and everything was happy.  Even though I did this:

net groupmap modify ntgroup="Domain Users" unixgroup=users

I still cannot set users as the owner.  i even created a user called users 
and tried to fake it, but no dice. 

Ideas?

-Aubrey King