To use a multi-select list box as the criteria, you'll have to use VBA.
Attached is a demo DB. When some products are selected in the list box and the Show Records button is clicked, a query will be created and run. The code is contained in the On Click event of the button.
The code was written in Access 97 so DAO was used. If you write the code in Access 2000 or 2002, you must made a reference to DAO (when the code window is open, choose menu Tools, References... and select Microsoft DAO 3.6 Object Library from the Available References list.)
If you use Access 2000 or 2002, choose Convert and save as a new name when the attached DB is opened for the first time.
Hope it helps.