Microsoft's Mac Business Unit released a patch for Office for Mac 2008 SP2 that fixes an issue the suite had with opening XML files created in some (other) versions of Office.
The company said that the update applies to: Office 2008, Office 2008 Home and Student Edition, Office 2008 Special Media Edition, Word 2008, Excel 2008, PowerPoint 2008, Entourage 2008.
The patch is a 23.8MB download from the MacBU's Web site, and it is officially named Microsoft Office 2008 for Mac 12.2.1 Update. You can also download it through the Microsoft AutoUpdater utility in Office (accessed under the Help menu of any of the suite's components).