Microsoft released the final version of the tools required for use between Office 2007 and Office 2003. If you are using Office 2007 and saving the files in the new xml format then you will need to have your users (who are still using Office 2003) to view the files.
Compatability Pack for Office 2007 File Formats.
http://www.microsoft.com/downloads/details.aspx?FamilyId=941B3470-3AE9-4AEE-8F43-C6BB74CD1466&displaylang=en
2007 Microsoft Office Add-in: Microsoft Save as PDF or XPS.
http://www.microsoft.com/downloads/details.aspx?FamilyId=4D951911-3E7E-4AE6-B059-A2E79ED87041&displaylang=en
