Sure you can run your own DDNS server on 2000-2003 server. IIS does have some limitations though that prevents standard update formats like those of no-ip and dyndns.org.
You simplest bet for 2000-2003 server is to use a pre made package like MintDNS (http://www.dyndnsservices.com
) MintDNS has solved all the standard update incompatabilities found in IIS. The creators of MintDNS used to run the address.net DNS service many years ago, and was one of the first along side ml.org and dynip.com. They boast some services using MintDNS provide dns services to millions of users. The software leans towards the DVR IP camera market, but can be easily modified to suite any needs you may have. At $250.00 I think its a steal.
There sre also some pre made Linux packages like GNUDIP,
Also I have tried this before, and the DNS WMI will not accomidate very many users. Your best choice for Windows server is to use GSS-TSIG which is what MintDNS uses, but was a little beyond my understanding.
Anyhow best of luck with your project.