MSIE is trying to append a file extension based on the web server supplied MIME type, assigning "zip" for unknown types. Because P4Web versions prior to 2007.3 do not have MIME type entries for the office 2007 extensions, users encounter the zip file problem when they use MSIE with P4Web and Office 2007 files that have the new extensions. There is an option in IE to disable this feature, but then IE treats Office documents as type "text" and attempts to display them in the browser.
Users encountering this problem have several options:
Avoid using MSIE: FireFox and Safari handle the new file types correctly, for example.
Change the extension after downloading -- the file contents are correct.
Use P4Web 2008.1 or later.
The affected extensions and appropriate mime types for Office 2007 and later are: