Mail delivery to and from Exchange Server 2003

Greetings.

We have a plain old POP3 Mail Server (Type InstaGate EX2) sitting on our gateway in a black box which is also a firewall. Within this box, I have the option to "forward all incoming mail to an internal SMTP server". Since I have an Exchange 2003 server sitting on my LAN doing mainly groupware stuff, I would like to do just that. However, I am not sure how to go about doing this on the Exchange Server.

Basically I want to accomplish 2 things:

1) Configure my Exchange 2003 Server to act as an SMTP server and recieve Mail from the blackbox on my gateway
2) Have the Exchange Server send Email directly to the internet (currently, the blackbox is handling the recieving (POP3) and sending (SMTP) of all mail traffic going to the internet)

On the client side in Outlook, the users currently have 2 services activated:

1) POP3/SMTP to communicate with the blackbox for mails going to/from the internet
2) Exchange Server to handle LAN-internal mail and groupware stuff

Ideally, after pulling this through, I would like to end up with the Exchange Server Service in Outlook only.

Can this be done? It would be great if someone could tell me what to do on the Exchange Server since I don't know it very well.

Thanks and regards

Boris