OfficeTab is a freeware tool that lets to add tabs to Word, Excel and PowerPoint from the Microsoft Office suite and is compatible with both Office 2003 and Office 2007 on XP, Vista and Windows 7.
The advantage of using Office Tab is that it enables you to open multiple documents very easily within one office window. You can switch between different tabs very easily by just with a mouse click or keyboard shortcut.
There are several options to configure the tool according to your choice like color and appearance of tabs, tabs position, etc. [via]