Security in Access can either drive you crazy or be your savior. If you understand and follow the rules for setting up and maintaining security, it can be a great tool to work with. But if you don't pay attention to details, problems can arise when you try to access objects in your database. Access gives you a number of ways in code to solve various situations that can arise when using security.
Please note that almost all this material applies only to Jet/MDBs. For SQL Server/ADP security, you should make an ADE file and use integrated SQL Server or NT security to protect your data.