Here is a way to swap between two workbooks. It is not very elegant, and hopefully someone else will have a better way of doing this!
This method uses the Workbooks collection, and iterates through the collection, activating the one that does not have the same name as the current active workbook (and ignoring PERSONAL.XLS).
Private Sub chWB()
Dim rngWB As Workbook
For Each rngWB In Workbooks()
If Not (rngWB.Name = ActiveWorkbook.Name Or rngWB.Name = "PERSONAL.XLS") Then