In your database you have a section called Macros, If you are using Access 2003 or lower on the left is a section called Macros, and you create a new macro from here.
If you are using 2007 or 2010 then select the Create Tab and on the Right you will see Macro, just click and Select New Macro then you will see some lines and it should say Action, click the first action and select the drop down and then search for Open Form once you select it the Arguments will be displayed and you then select the form name, then create the Next Action and search down the list for Maximize. Then save the macro as suggested as AUTOEXEC.