Are there compatiblity issues with Office 2007 and previous versions?
Yes. Microsoft has added the new Office Open XML Formats to Excel, PowerPoint and Word 2007. This means that if you save a file within Office 2007 (default), it is saved as a new XML extension. Previous versions of Office suites will not be able to open these files, until the Microsoft Compatibility Pack is installed. (Word 07 saves files as name.docx instead of the usual name.doc, Excel saves files as name.xlsx instead of name.xls, etc.) The other alternative for this issue is to use the Save As option in the 2007 application and choose to save the file in an older format.