WebDav acces password

Hi,
I have Windows Server 2003 with IIS and WebDav mounted. I can access to the
webdav directories at https://xxx.xxx.xxx.xxx:444. The autentification is
windows integrated and works fine. Only I have a message that the certificate
of the server is not from trusted certification autority, it is only for
local purposes.

The problem is when the client connect, is asked for a username and password
and every time when hi open the file and to save the file. for every file
every time
at open and at save file.

Is there some way that when the client is connected and autentificated to no
ask more for username and password.

Thank you in advance