By default it is not possible to connect to webdav resources without SSL encryption in Windows 7. To enable unencrypted connections (http and not just https), follow these steps:
Press the keys [Windows] + [R] to open the windows command line and enter
regedit
to start the registry editor. Then go to the registry branch:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WebClient\Parameters
and change the value for "BasicAuthLevel" to "2" (decimal). Then restart Windows.