Here are details on changing TS ports:
(Bob, I hope to learn from your experience.)
I should add that you *can* have the Terminal Server listen on the external interface of the ISA Server IF you change the listening port number. If you change the listening port number that TS listens on, you'll have to change the TS client configuration file for that connection in order to make it work. If believe (but have not tested) that you can publish multiple internal network Terminal Servers if you change their listening ports, change the client config file, and then create Protocol Definitions and Protocol Rules for the new TS listening ports.
HTH, Tom www.isaserver.org/shinder