You could use this status bar in execution mode.
http://christopherjmcclellan.wordpress.com/2014/03/08/progress-bar-for-ms-access/
It's a bit much to post here in it's entirety, but it relies on two big things. The first is that you can create a new instance of any form on the fly in your code. This hinges on the fact that Access forms are really just glorified class modules. You can try it yourself by saving a new form with the default name "Form1", and then placing this code in a regular *.bas module.
Sub ShowForm()
Dim frm as New Form_Form1
frm.Visible = True
Stop
End Sub
Note that I put a breakpoint in because the form will auto-destruct when it goes out of scope.
The second big thing is using DoEvents to give the OS enough time to repaint the screen.
Understanding these two things, you should be able to design a form with a textbox that changes size as your process runs. Also, I would actually recommend a UserForm instead of an Access Form. I didn't know it at the time, but you can use UserForms not just in Excel, but also in Access.