To make a quick copy of your current spreadsheet, go to View and choose New Window.
Pete
Start another instance of Excel, and open the file again (if it's already open in the other instance it will open as read-only).
~ or ~
Stretch the one instance of Excel across both monitors and arrange your windows (not sure how to do that in 2007 though).
What the logic of how Excel determins which instance to open a file in?
If you've opened another instance of Excel, simplest thing is to open the workbook from that instance, not from Explorer.