This pertains to Windows Vista and Windows 7 only. If you are running Windows XP then stop reading.
If you are running Vista or Windows 7 and you are attempting use the “Upload Multiple Documents” feature of MOSS 2007 or WSS 3.0 to upload zip files you have probably noticed that zip files do not show in the upload explorer window. The “Upload Multiple Documents” feature is an ActiveX control that installs with Office 2003/2007 so if you aren’t running either Office versions then the option won’t show up in SharePoint. The problem with zip files and the ActiveX control has to do with how Vista deals with zip and CAB files. By default Vista is configured to show zip and CAB files as folders allowing the user to drill into their contents within Windows Explorer. For this reason they do not show up in the ActiveX control that handles multiple file uploads for SharePoint. To fix this problem you need to delete the following registry keys. WARNING! Backup your registry before making any changes!
Now deleting the above registry keys is a bit more involved than running RegEdit, finding the keys, and deleting them. Both keys above are protected keys and are own by the SYSTEM account. In order to delete the keys you need to change ownership of the keys, delete sub keys first, and then delete the root key. To do this you need to download the PSExec utility from Microsoft that is part of the Sysinternals tools. The download is located here http://technet.microsoft.com/en-us/sysinternals/bb897553.aspx . Once you have downloaded the tools and extracted the PSExec utility from the zip file, you need to then start a windows command prompt as the local machine administrator (if you are not logged in as the administrator then run the following from the RUN dialog: runas :user/localhost\administrator CMD ). Once the command window launches navigate to the directory where you unpacked the contents of the zip file that you downloaded earlier and execute the following command: psexec -i -d -s c:\windows\regedit.exe. At this point you are now running RegEdit as the SYSTEM account and will be able to change ownership of registry keys. It is important to note that you have to delete child keys before deleting the root key.