I'll be most interested to see if anyone has an answer to this; I've been
trying to figure it out for a while now. I finally gave up and "rolled my own!
" It requires placing a large text box (call it ZBox) on your form. Assign it
the same Control Source as the field you want to expand, and make it visible
by double clicking the field you want expanded.

Substitute the actual name of your field to be expanded for YourFieldName.

Private Sub Form_Load()
    'Make the textbox invisible on loading the form    
     ZBox.Visible = False
End Sub

Private Sub YourTextBox_DblClick(Cancel As Integer)
   'When you double click the field, this make the ZBox
       'visible and moves the cursor to the beginning to
       'deselct the text  
       ZBox.Visible = True
       ZBox.SetFocus    
       ZBox.SelStart = 0
End Sub

Private Sub ZBox_DblClick(Cancel As Integer)
       'Double click the ZBox to close it and
       'return to your original field
   Me.YourTextBox.SetFocus
   ZBox.Visible = False
End Sub