How to use 2003 Additional Domain Controller after failing 2003 Primary Domain Controller

Hi Experts,

I am new in Active directory services.............

We have a single window 2003 domain controller with Exchange server 2003 which is used for mailing and
Second window 2003 server which is ADC. Now i am Planning to configure ADC for Failover.
I want to know some informations which is related to my task:

1. If Primary Domain Controller Fails, then ADC will takes control Manually or Automatic ?

2. Difference between Seize and transfer role ?? what will perform in my case ?

3. Plz tell me whole method from starting step by step in simple way so that i can
   understand at once.

4. One confusion from long time is that all existing clients are joined with primary domain name or ip
   if primary DC goes fail then would i need to add all computers with ADC ip address again ?? i am
   thinking this bcoz Primary DC and ADC ip address are different
 
   Primary Dc = 192.168.1.2

   ADC = 192.168.1.5

   correct me if i am wrong .......