I have implemented a back button in my db,
Basically I created an unbound form that has an unbound text box. When firing up the db, it opens this form and hides it so users can't see it.
All you need to do then is for each button pressed, add some vb code to post the form name you are going from into this hidden forms text box.
In the back button on click code, refer to this value.
eg
If the hidden form is called backform and the text box is called back, on each button pressed the code to enter would be
Backform.back.value = "Formname"
Then the code for the back button would be
Docmd.close acform etc
Docmd.openform Backform.back.value
Hope this helps