Hi again,
I've got this tutorial about webdav from the d-link team last week:
ftp://ftp.dlink.de/dns/dns-325/documentation/DNS-325_howto_verALL_WebDAV_de_140911.pdf
It works for me like a charm!
It is in German but there are a lot of images so you should be able to follow it.
It uses HTTPS and not http and for windows 7 you need an external webdav client like bitkinex.
Furthermore you should use the "map a network drive" option under Windows XP and Vista.