Access Security Basics: http://www.jstreettech.com/files/AccessSecurityBasics.pps
Access User Level Security (ULS) has been deprecated for the ACCDB file format, but many people are still using ULS for their legacy Access MDB applications. Here is a PowerPoint slide deck that Armen Stein, President of J Street and Access MVP, has presented to Access user groups. It describes various approaches for securing an Access database with ULS, with some common mistakes that developers often make and tips to avoid them. PowerPoint file, 139k.