From Noah Horton ...

Have you ever wanted to be able to find and connect to your computer across the Internet, but did not want the complexity and cost of buying a domain name and using Dynamic DNS? With Windows Vista, you can use Internet Computer Naming.

More

Is there a central server? The cool answer is that no, there is no central server. The whole service is peer to peer based on a technology called PNRP ... basically, every machine knows about a few other machines basically at random. Those machines know a few others, who know a few others, etc. When I want to resolve someone else's name, I can use all of those relationships to track down the machine publishing the name I want.