Even in earlier versions, you wouldn't normally want to set your default
workgroup to a secure one. You'd usually use a desktop shortcut to launch
the secure database.
Security is still supported for the mdb file format in 2007, but not the
accdb format. You can use a desktop shortcut, or you can start the
workgroup administrator via Database Tools...Administer...Users and
Permissions or in code
DoCmd.RunCommand