Is there any way to open the new Office 2007 file formats in older versions?
Microsoft Office 2007 introduced a new set of file specifications known as Office Open XML format. These XML based file formats greatly improve document interoperability between Microsoft Office documents and other applications.
Because the standard is based on universal XML technology, it can easily be added to older versions of Microsoft Office. Microsoft provides a compatibility pack for adding these new file types to your existing Office version.
Before downloading and installing the compatibility pack, you should install all High Priority updates for Microsoft Office.
The Compatibility Pack works for all Word, Excel, and PowerPoint versions 2000 and newer and can also be used with the associated Viewers.
For more information, please read the following Knowledgebase Article: