In the On Change Event for the textbox for ID number use DLookup to populate the other relevant textboxes such as:
Me.Yourtextbox = DLookup("[fieldToReturn]", "TableOrQueryname", "[IDnum] = " & Me.ID)
Me.YourNexttextbox = DLookup("[fieldNextToReturn]", "TableOrQueryname", "[IDnum] = " & Me.ID)...