VPN…Outlook2000

Hi;
I use w2k vpn client to access my employer network. When ever I launch outlook, it asks me for user name, PW, and domain name . I checked the box under security which says ” Automatically use my windows logon name and PW (and domain if any), this did not help at all. Please help if you know how to stop the “Enter Password” box from poping up evry time I launch outlook…It happens only when I do VPN.