This is quite straight forward.
1. Setup a workgroup using MS Workgroup Administrator.
(usually found in C:\Program Files\Microsoft Office)
2. All PC's that share this database then need to run the
above program and they need to join the workgroup you've
just created.
3. From Access, click the Tools menu then Security, then
User & Group Accounts. From here you need to setup
accounts for all those people who are going to use the
database. Each person can then have their own password.
4. Then apply permissions to each of these user accounts
and let some people have read only and others can have
full permissions.
5. You should be the administrator and have the admin
password.
N.B. You can set permissions for everything, Forms, Tables
etc.
I've just applied this level of security to a database
i've created in work and it works perfectly.
Hope this helps.