Office Tab – If you enjoy using tabs in your browser then you will surely appreciate this Office plug-in which provides similar functionality in Microsoft Office 2003, 2007 and 2010 (free version includes support for Word, Excel, PowerPoint).
After installing Office Tab you can; enable or disable tabbed support in each application, move the tabs to the side or bottom, and change the appearance of the tabs with a number of styles to choose from. You can right-click the tab bar to add a new document tab, and each time you open a document it will be added to a new tab automatically.
There is a version comparison chart on the home page, I think you’ll find that the free version will provide ample features for most.