Windows 2003 server replication/clustering

Hi,

I have two windows 2003 servers with static IPs. I want to shift online applications that are running on serverA to serverB in case of any failure. Applications running on serverA are integrated to many remote services with serverA IP address. How the applications will be remain in runing state if passive serverB become active(as serverB has different static IP). How can i accomplish my task, either using replication or clustering or something else.

thanx

Mazhar