Mack2,
There is a faq on Access security here, that will be more in-depth. The short of it is, there is already a workgroup file (system.mdw) upon install. The default user is always 'Admin', and the default pwd is blank.
If you change the admin pwd to anything non-blank, then any .mdb that doesn't have a shortcut pointing to some other .mdw will ask for pwd. Also, if you change the default .mdw (by using Wkgadmin.exe), all .mdb's opened without a shortcut pointing to some other .mdw will open with this .mdw--and if this .mdw's admin user has a pwd then you'll get a prompt there too.
--Jim