The problem is related to incorrect hinting of the webserver, tricking IE7/8 into believing you are in fact downloading a ZIP-file, rather than an Office 2007/2010 file. The reason for this is because these files are in fact XML-files, compressed to a ZIP, but have a different extension, indicating it's not a regular ZIP-file.

There are two ways to fix this. The best way would be to change the webserver (if possible, ask the administrator of the webserver you are downloading from) to add the correct MIME-types, so the webserver provides correct hinting. How this is done, depends largely on wh  ...