Set up User-Level security so everyone has to log in.
Turn off the database window on startup and turn off the bypass.
Create an autoexec macro that opens the form based on their UserID.
Only give them access to their forms.  You will also have to take away
access from the table and the query if your users are smart enough to try to
go around you and open them directly.

The following links might help...

Bypassing shift key...
http://groups-beta.google.com/group/microsoft.public.access/browse_thread/thread
/f03ffccf6a008452/efdeb1dad6e2bef9?q=microsoft.public.access+bypass+shift&rnum=4
&hl=en#efdeb1dad6e2bef9

User-Specific Forms...
http://groups-beta.google.com/group/microsoft.public.access.formscoding/browse_t
hread/thread/29248b5452b3ba61/a35305f4d737266e?q=microsoft.public.access+autoexe
c+user+forms&rnum=4&hl=en#a35305f4d737266e

Similar post on User Forms...
http://groups-beta.google.com/group/microsoft.public.access.forms/browse_thread/
thread/364390a9c1b66a49/df1702f0858b3e7f?q=microsoft.public.access+autoexec+user
+forms&rnum=19&hl=en#df1702f0858b3e7f

Security FAQ...
http://support.microsoft.com/?id=207793

Security White Pages...
http://support.microsoft.com/?id=148555

A post on taking away access to the table, but still allowing updates
through a form...
http://groups-beta.google.com/group/microsoft.public.access.security/browse_thre
ad/thread/10894bd14de2d95a/0dff4a869a52df72?q=microsoft.public.access+query+run+
owner+permission&rnum=4&hl=en#0dff4a869a52df72

And one more...
http://groups-beta.google.com/group/microsoft.public.access.gettingstarted/brows
e_thread/thread/6f017cd2870defdf/753a4ec9bcb39700?q=microsoft.public.access+quer
y+run+owner+permission&rnum=61&hl=en#753a4ec9bcb39700