Nice work!
In some limited testing I have able to drag and drop from Windows into folders in the admin personal workspace.
I cannot create folders via webdav since there really are not folders in FengOffice, a workspace's documents object acts like a folder for the workspace. So it makes sense that you cannot create a folder via webdav. Not a big deal.
Via Windows Network Connection I can connect to the webdav as a "web folder." I can connect with accounts created in FengOffice but I end up in the admin personal workspace regardless of the FengOffice account used and I can add files to the admin personal webdav folder, something that shouldn't happen. I cannot login or access anything using AD accounts. I can login to FengOffice with AD accounts but I cannot access webdav with the AD accounts.
**** Note: Using Nautilus in Gnome, I can connect to FengOffice user personal workspace and not the admin personal worksapce.
In Firefox, and Internet Explorer with Show Friendly HTTP Error Messages turned off, I get the following when trying to connect to the webdav folder:
*** I just checked the SabreDAV site on code.google.com and apparently this message indicates SabreDAV is setup correctly?
<d:error>
<s:exception>Sabre_DAV_Exception_NotImplemented</s:exception>
<s:message>GET is only implemented on File objects</s:message>
<s:sabredav-version>1.2.4</s:sabredav-version>
</d:error>
So while there are some issues this does look promising.