The difficult I do immediately, the impossible takes a little bit longer.
Forms
Log-On form (Control what Form your Users see)...
Disclaimer ...  This Log-On form offers * no *   security or protection of your data or design elements or code of any kind.  It use is to demonstrate how to control what the User sees when they log-on to the database. For security see links at the bottom of this page...
To implement this, first, you're going to need to add two fields to your table tblUsers (or whatever name you have given to the table that holds your Users information)...
1. uSecurityID - FK (Number, Long)
2. uPassword - (Text, 15 [or whatever length you want])

Second, add tblSecurity to your database...

Fields for tblSecurity
sSecurityID - PK (Number, Long)
sClearance - (Text, 25)
Lastly, download Access 2003 sample (or Access 2010 sample) file and copy/paste the code, changing the names of the tables and fields to match yours to implement.  To see another way to control what your Users see without requiring them to Log On everytime, click here.
How does it work?

Simple, open the Log-On form (passwords on the form)...  Once you log-on the Control Center* below opens while making the Log-On form invisible.  It then holds the value of the User (Login ID) on the Control Center (or anything else you want to control) to use for filtering.

Note, you will want to add some additional Error Handling.  You will also want to set your database so the Log-On form opens when first opening the database and disable the built in Close, so your Users can't bypass the Log-On form.

* In the screen shot below I logged on as User
Access 2007 to 2010
Make Controls resize with a form  (Access 2007 and higher)
Switch Windows  (Access 2007 and higher)
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