You can create your own Form but need to set it to a table which holds all the employee details and passwords then on your form you could have a drop down to allow the user to select there name and then they add there password with a couple of unbound textbox you can check against the entry if it is correct allow them access if not then give them a nice message stating they either haven't used the correct password or don't currently have access rights and should contact the database administrator for permission to gain entry.
Then you create a macro to show the form on start up and name it autoexec.