I have an append query that takes several minutes to complete. Is there a way to display a msgbox saying "Working" and when the append is complete to say "Update Complete".

Hi,
Create a custom form with a label on it that says what you want. Then open the Form before you execute the query and change the label's caption to whatever you want after it has run. You could also then reveal a close button that you had hidden while the query was running.
HTH
Good luck

Is there a code that would close the form after the append is completed?

Sure...:

DoCmd.Close acForm, "YourFormName"

HTH
Good luck