Moving Exchange into exisiting network

We have a merge happening where we will need to bring in an Exchange server into our existing network that does not use Exchange. There are not many mailboxes there, but not being that familar with Exchange 2000, I’m looking for resources on making sure the move is smooth. Once they are inside our network what needs to be done to ensure delivery of service? Our existing network is Windows 2003 on AD. We have a firewall but no room (no more available IP addresses in our DMZ). I’m not sure how to have the Exchange server communicate with the outside world.