Windows systemwide password control

My question is basic.  I have Server 2008 SBS.  There are 4 computers connected with Vista.  I have set up user folders for 3 users, and set up the sharing so that each person can only see their folder.  To do this, I had to set the password on the server, and then set each user's Vista logon to be the same thing.  I know that it is possible for the user to change their login password, and for that to synchronize with the server to change the password to the shared folder.  My problem is that I don't know what to research.  Is this what User Access Control or Active Directory are for?  I don't mind the research if someone can please tell me the correct terminology to search for.  I am extremely grateful for any help.