Citrix and Windows 2000 Professional DU

Have a Windows 2000 Professional PC setup for DUN. Was initially having a problem doing DNS resolution back to our NT 4.0 network but resolved that by changing a DNS setting under IP protocols to the full domain name. Problem I'm having now is getting Citrix ICA (v4.21) client to work. It asks for a user ID and password and attempts to connect to the Citrix farm but nothing ever comes up. I tested the same user ID and password against a Windows NT 4.0 workstation also using DUN and it works just fine so its 2000 related.