How to Implement a New Server on a Existing Network?

Hello,

We currently purchased a new server for our network as the old one has been nearing its last legs. Our old server was running SBS 2003 and then new one is being fitted with SBS 2011.

My question is the following:

How process do I have to do to connect the new server to the network and then retire the old server?

Thanking anyone for help in advance.

Rohan