Windows NT Terminal Server/Terminal Serv

I have a small company that has two to three dial in users accessing the network with modems and deticated PC anywhere work stations.
A Consultant I work with thinks could move to a Single Server running Windows 2000 Server utilizing there built in terminal services over the internet. I wonder if we should use NT 4.0 Terminal server or if Terminal Services of 2000 Server is enough. And can I increase speed of use by running Citrix metaframe on top of either one of them?