1. Register for a domain name
2. Choose a registrar that lets you customize DNS settings for your domains.
3. Register for a free hostanme id dyndns.org (e.g. myownpc.homeip.net)
4. Set original domain name's DNS
domainname.com should be CNAME myownpc.homeip.net (normally it is xx.xx.xx.xx i.e. IP address or "A" record)
DomainName.com -- Reserve Your Place In Cyberspace with DomainName.com Domain Name Registration Services! should be defined the same as domainname.com
Any registrat based on "enom" API would let you do that. I have used $2.85 Domain Registration : Register or Buy Domain Name Registration & Cheap Domain Transfer in past
5. Download software for updating IP of myownpc.homeip.net whenever you get a new IP

Thnank you Channel9