Opening up Office 2007 files in Office 2003 and XP
The Microsoft Office Compatibility Pack for Office XP and Office 2003 enables a user to open and even save 2007 Office release XML files. That's cool and reduces the risk when you have some folks using Office 2007 in your company, and others note. Nice feature.
http://technet2.microsoft.com/Office/en-us/library/c6189fcd-3668-4cd7-8bac-5c37e338bde21033.mspx?mfr=true