When Microsoft launched Office 2007 it came with a new set of default file types that couldn’t be opened by previous versions of Office or by other office suites.  If you are affected by this then there’s a simple fix for it, depending what software you use and what type of computer you have…

You use Office XP or Office 2003 on a PC

You will need the Office 2007 File Format Compatibility Pack that you can get here.

You don’t have Microsoft Office on your PC

The latest version of OpenOffice is fully compatible with the new file formats.

You use Office:Mac 2004 on an Apple Mac

There is a patch for Office:Mac 2004 that will allow you to use the new formats here.