Having problems opening Office 2007 documents because you still have an older version of Office? By installing the Compatibility Pack from Microsoft in addition to Microsoft Office 2000, Office XP, or Office 2003, you will be able open, edit, and save files using the file formats new to Word, Excel, and PowerPoint 2007. The Compatibility Pack can also be used in conjunction with the Microsoft Office Word Viewer 2003, Excel Viewer 2003, and PowerPoint Viewer 2003 to view files saved in these new formats. For more information about the Compatibility Pack, see Knowledge Base article 924074.
The MS compatibility pack can be downloaded here.