How to automatically toggle between applications?

Our call centre (only 8 users) have an application running on an XP workstation that displays on a big wall mounted TFT showing how many calls have been answered or are still waiting to be answered. They now want to also show an Excel spreadsheet on the same display and have the two items automatically toggling between each other.

Can anyone suggest a way of doing this via XP or a third party application that would do it?