Office 2007 Compatibility Issues
Microsoft Office 2007 uses a XML based format and extensions for new documents, spreadsheets, workbooks and presentations created by Word 2007, Excel 2007 and Presentations 2007. These new file formats, docx, xclx, pptx, etc. are not backwards compatible with older versions of Office. This means that older versions of Office (Office 2003, Office XP and Office 2000) cannot open and read files using the XML format.
To solve the compatibility issues of new XML based Office files between various versions of Office 2007, 2003 and 2002 (XP), Microsoft has released the Microsoft Office Compatibility Pack. Installing the Microsoft Office Compatibility Pack on the computers using Microsoft Office 2003 or Office XP (2002), will allow the user to open, edit and save documents in the new 2007 XML formats.
You can install the compatibility pack on a computer that is running Microsoft Office 2003 programs, Microsoft Office XP programs, or Microsoft Office 2000 programs. When you install the compatibility pack, you can open, edit, save, and create files in the robust Office Open XML Formats.
Be sure that Microsoft Office updates are current before installing the Microsoft Office compatibility pack.