I believe that for .com, .net, and .org at least, you still need two or more DNS servers. Your registrar may be willing to provide a "slave" DNS server for you (mine does) either free or for a small fee. Otherwise, you'll have to make arrangments with your ISP or some other provider of DNS services. You could also provide both servers, if you have multiple machines with static IP addresses.
Once you have the DNS servers set up and ready to go, you just tell your registrar to switch the domain over onto the new name servers. Mine has a nice web-based control system that lets you just do all this. Your experience may vary.
You can easily get somebody to host the name-service for you. If you do, make sure you get a * alias for your domain, so any whatevernameyouwant.domain.com maps to the server's IP address. That way you can make as many virtual hosts as you want under the same domain.