Office 2007 has changed its format. The files are now zip files with xml inside. Additionally they placed an x at the end of all extensions. You can't open these files with the old applications. Here's Microsoft's treatise:

http://msdn.microsoft.com/msdnmag/issues/06/11/basicinstincts/default.aspx

It would be great if these new files can be indexed by Confluence or for that matter Jira, though admittedly the unzipping would be expensive.