Two workbooks, one Excel session

Not a deep programming question, but an issue I am having.

Windows XP, SP2
Excel 2003, SP2

Until recently I was able to Alt+Tab between multiple Excel workbooks, which were stored as separate tasks on my Windows taskbar. For some reason I am now given only one Excel session and I have to select the Window menu in Excel, then the workbook I want in order to switch over. I haven't installed anything recently so I have no idea what caused this. Any help in getting me back to my Alt+Tab glory days would be greatly appreciated.

That certainly allows me to nav within Excel and I didn't know about that. However I am trying to see about returning the old Alt+Tab functionality so I can navigate all of the windows sessions I have open without having to shift to another keystroke. Does anyone know how to accomplish this?

That did it! Thank you so much, my sanity is restored.