I'm with redwoodly on using Jet Security, but go the whole hog. Create a custom Workgroup Information (mdw) file and new database based on your old one. It's easy and will save you grief in the long run:
1. Open wrkgadm.exe and create a custom Workgroup Information (mdw) file. Make a note of all PIDS and the address of the new mdw file.
2. Open Access only (using this mdw file). Do not open a database file.
3. Go to Tools>Security>User and Group Accounts and create a password for the default Admin account.
4. Create a new user account with a non-zero length password. Make a note of the PID. Add the new user to the Admins account. You should logon using this account.
5. Create new group accounts based on your organisational structure (or other scheme).
6. Create new user accounts in the names of those who want to access the database amd make sure they all have passwords. Assign these user accounts to your custom groups.
7. Save all changes and close the dialogue box
8. Close Access and open it again using your new custom user account (created in step 4).
Now you need to create a new database based on the old mdb file:
1. Go to File>New. Using the New dialogue box create a new database.
2. Go to Tools>Security>User and Group Permissions and assign all possible permissions for all new database objects and the database to your account
3. Assign the desired permissions to the custom groups.
4. Remove all permissions for all database objects from the default "Users" and "Admin" group accounts
5. Save all changes and close the "User and Permissions" dialogue box.
You have now set the permissions the database and for all new objects created by you or when objects are imported into the database. To import objects form your old database:
1. Go to File>External Data and in the "Import" dialogue box find your old database file, elect it and click on OK.
2. In the Import Object dialogue box select all database objects in all object categories (Table, Form etc.)
3. Click on the "Options" command button and make sure the "Menus and Toolbars" check box is checked (so you'll import any custom commandbars you created) and clik on OK.
4. Go to Tools>Startup and in the "Startup" dialogue box set the properties to those in your old database file (remembering to hide the database window and uncheck the use "Use Special Access Keys" check box - click on the "Advanced" command button).
I'm assuming that you have a back-end file (tables etc.) and a front-end file (forms). You have to do this for both and recreate linked tables pointed at the back end file in the front-end database.
Not all users will be happy if you set the Workgroup information file to the one you've created. There will be the usual howls of protest about using passwords for other Access databases. So to force users to open your database with the correct workgroup information file create an application desktop shortcut:
1. Create a desktop shortcut pointed at your new database file.
2. Right-Click on this and type in the full file paths in quotes of the local Access executable (or run-time version), database file, and workgroup information file including the /wrgrp command prompt:
"<Access>" "<database file>" /wrkgrp "<workgroup information file>"
3. Clear the "Start In" text box and click on OK.
Copy this Desktop Shortcut and new front and file to all your users machines and tell them what their new user accounts and passwords are.
There are further refinements about hiding or revealing items on menus (command bars) or switchboards based on object permissions, but that's another (longer) story. Feel free to ask.