If you downloaded the previous beta versions of Office 2007 then it replaced any previous installed versions potentially creating compatiblity issues with documents from earlier versions of Office. The solution as discussed on ComputerWorld is to have the program(s) running in your browser and voilà ! no more those issues...
Among the programs availble to test from Microsoft Office 2007 are Access, Excel, InfoPath, OneNote, Outlook, PowerPoint, Project Professional, Publisher, Visio, Word...
As the article says this is a first in browser-based Office beta !