Split your database into a frontend component (forms, queries,
reports, etc) and a backend component (tables only). The backend
belongs on a shared folder on your network server, while each
workstation should have its own copy of the frontend.

http://www.granite.ab.ca/access/splitapp/index.htm

Once you have split the database, you will want a method to
automatically distribute any modifications to the various
workstations. Many people use:

http://www.granite.ab.ca/access/autofe.htm

Distribute the FE as an MDE file instead of MDB file. No changes are
allowed in MDEs.

Implement Access UserLevelSecurity on the BE, and allow ReadData
permissions to all the tables to the Users group, but deny them the
permission to modify the table structure. By allowing Users to enter
data, then anybody using an unsecured workgroup file will be able to
login as the Admin user and have permission to modify the data.

Access user security is not to be taken lightly, so read very
carefully and thoroughly, practice on a COPY of your database, and
don't skip any steps in the process.

Here are a number of links about security:

http://home.bendbroadband.com/conradsystems/accessjunkie/resources.html#Security

--
jackmacMACdonald@telusTELUS.net
remove uppercase letters for true email
http://www.geocities.com/jacksonmacd/ for info on MS Access security