NT4 PDC to Server2003

so i have read loads of post on this subject but none seem to fit my circumstances. i have walked into a new position and the infrastructure is ancient. they have a NT4 PDC, no BDC, they have never heard of AD (later project)completely fixed IP site. we absolutly must keep the same name and ip, this is an authentication box only.

my question is, can someone advise on this proceedure i have to present a breakdown of tasks to the team and am slightly worried about this.