Disclamer:
I'm NOT a Linux/Ubuntu user. This information, while been somewhat relevant, may not be totaly correct.
When using Ubuntu, or any Linux distro, each user have his own separate home folder. That folder contains all of his personal configurations and is totaly invisible to all other users except the administrator, also known as "super user" or su.
Compared to Windows, the default acount is a regular user acount with limited rights.
The cifs config of a given user should reside in his home folder. That way, it's only used, and accessible, when that user is loged in.
When loged in as super user, you should lock that file so that the user can't change it and stay limited to the areas that are alowed to him.
From the second user acount, do the search and mounting of his personal remote folder.
You should access some Linux and Ubuntu forum to get more thourough and specific informations.
Electro, October 2011