Recently I upgraded my company Active Directory infra structure from 2003 32bit to AD 2008 64bit. I save all the procedure in this small howto. I first test the whole scenario in a VM environment, and then implemented it on Live Production Servers. This guide was written so that it may be helpful for others and also it will be reference guide to me for future retrieval.
My Current Scenario:
Windows 2003 (x86) Domain Controller
Windows 2003 (x86) Additional Domain Controller
I first uninstalled the ADC to make things simpler.