Internet Email with Exchange Server

On my network, I am trying to brin up an exchange 5.5 server. I am able to send/recieve messages using exchange client without a problem. My problem is trying to pull in internet email for my clients. I know Exchange has this capabilty but does it require IMS. I do have DSL but this server is not connected to that connection. It is using proxy like other client to go out to the net. Please give suggestion or web links

Thanks