Cobalt Qube 2 and Office XP

We’ve been supporting Outlook 97 and Outlook 2000 clients on our Qube 2 for years. Now I go to install Office XP, and Outlook XP, and the same configuration can’t find the POP3 server. Uninstalling XP and re-installing 2000 gets it to work again. What could be the problem? This was on a Windows 2000 Dell machine.