Accessing PPTX, DOCX, XLSX Office 2007 Documents (OpenXml) in Older Versions of Office
Attention Office XP and Office 2003 users! With the Office Compatibility Pack ... you will be able to open, edit and save documents in the new Office 2007 (OpenXml) format. Installation files here:
Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=941b3470-3ae9-4aee-8f43-c6bb74cd1466
Make sure you install all High-Priority update from Microsoft Update before downloading / install the pack.