Converting a domain controller is a really bad idea. If you must you, demote it first then convert it, but honestly your time would be better used creating a new domain controller and then replicating from the old one. There are so many things that can go wrong, I don't think you understand the undertaking you are asking here and the huge amount of things that can potentially go wrong and leave the client with out a DC while trying to get the thing to work. It is so much safer just to create a new one and then use AD to replicate what you want on over as if it was another physical machine.
Anyways if you do decide to try a p2v, this KB will help.
Virtualizing existing domain controllers in VMware vCenter Converter (1006996)
http://kb.vmware.com/kb/1006996
>>>" I think the bigger picture is that its really not advisable for your client to continue with Server 2003, its no longer supported and updates will not be released for it. Have you discussed other options such as Windows 2012 Essentials?I realize there will be a cost to licensing but your client has to understand this is a business cost, deciding to avoid by staying with old technology (virtualized or not) it not a good idea."
Yes, thank you. Using old software is how security breaches happen and expensive lawsuits. It is time to pull out the pocket book on this one.