[Samba] separating samba accounts from unix account?

[Ottensmeyer Joerg]

Hi,

is there any way to setup samba accounts (which then 
use a common share) but do not have a unix
account? 

the scenario is, that I want to support a goup of users
who have an "samba account" on my linux box and can
use a certain part of the filesystem as file server.
But I don't want to give them a unix account to ease
user management and avoid, that they can use other
services on the box.

I did not find anything about that in manual, FAQs, etc.
I would be grateful for any hint!

regards
-Joerg