Exchange 2000

Hi, I have a customer who has their own exchange server. It is Exchange 2000, running on a Domain Controller. They have a DSL internet connection unsing a LinkSys router, running NAT. They have a FQDN “company.com” and almost everything is workingfine.
Problem – Their ISP requires that all SMTP messages be routed through their SMTP server. Exchange 2000 is new to me and I have not been able to locate where to input the SMTP server to use for outbound messages. I know where it is on Exchange 5.5, but have not been able to find where on Exchange 2000. Can anyone help me locate where to enter the SMTP server to use? Thanks in advance.