Windows 2000 AD mixed mode upgrade

Hello Everyone.

We have :
2000 AD working in a mixed mode.
2 Domain controllers, one 2000 server and the second is 2003 server running Exchange 2003.

We are going to replace the old 2000 server with a new machine with 2003 server.

My question is:
What are the necessary steps to be taken to perform this upgrade?

Thank you