Do you have to enter a username and password when accessing the proxy via Windows? If not, are you sure there's any authentication going on with the proxy at all? I don't see anywhere to enter a username and password in my Netscape preferences, so I assume it's just popping up on you when you try to go somewhere, so I guess your proxy is requesting it.

Hmmm.

How is the SunPCI card networking set up? Do you have a network cable attached to the back of the card, or is it getting network access via the Sun workstation? If the latter, you should be able to run ``snoop -x54 -s10000 port <proxyport>'' (where ``<proxyport>'' is the numeric port number of the proxy server you're trying to use) from a shell on the Sun as root (use ``su''), then connect to the internet using the proxy from your SunPCI card and you should be able to see it authenticating itself.

I suppose that the real crux of the matter is what sort of proxy server you're using and what it's trying to use for authentication. Maybe it distinguishes between Windows and other OS clients somehow.