Authenticating to a WebDAV site externally

I'm trying to set up a WebDAV site so that an external partner can transfer
files to a server in ournetwork but not in our domain. I've set up the
WebDAV settings in IIS (using basic authentication) and punched out on an ISA
2000 server. If I test this internally, I can open the site as a web folder
and transfer files back and forth, but externally, the server won't accept
authentication when trying to open as a web folder; it will, however, allow
me to view the file listing when I connect to the site as a web page
externally. I've tried using NetBIOS name and FQDN - even IP address - and
it won't grant access. Any idea what I'm doing wrong?


Thanks in advance.