Exchange 2000 and ISA 2000

I’m trying to setup Exchange 2000 behind ISA 2000. I cannot find a procedure to make this work. I have three servers, all win2000, all DC. The main server has DNS. The ISA server has two network cards, one to the LAN, one to the DSL modem.
I already ran the ISA Secure Mail Server Wizard. Do I need ISA firewall client? Am I missing something else?
Thanks