You can use simple trick to deny users to open your database in MS Access and to see the content of database (tables, queries)...
http://www.access-programmers.co.uk/forums/showthread.php?t=51479[
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But remeber, first hide DB window on startup (Tools->Options menu).
This will not prevent user to see the objects in the database using another database (users can still connect to your database). So, Trilok Arora has right writing: "setting password is the only way to protect someone from accessing your database" ;)