Exchange 5.5 on 2000 Server

Can you install Exchange 5.5 on a Windows 2000 member server ? We currently have an NT Domain with Exchange 5.5 but because of server age want to upgrade the server. Have a budget for server but not Echange 2000.
On a test domain I've installed Exchange 5.5 on a 2000 server but cannot install Internet Mail Service. In the Internet Mial Wizard I get "The Internet Mail Service Requires the DNS Domain name to be configured". In NT4 TCP/IP DNS tab there is "Domain" do not not know how to confiure this in 2000.