Usually the folks that you pay for your domain will help you out in facilitating this. Basically for DNS (external internet facing) to work, the world (dns root) has to know that you are the authority now for records pertaining to the zones (domains) you are serving. Inverse (reverse) zones (in-addr.arpa) are somewhat more difficult because you'll have to find the authority of your particular IP ranges and get them to delegate your range out to your server.
This might help... but basically it'll tell you to go through the registrar ultimately used (often times you go through the person you obtained the domain thru...):
http://www.internic.org/faqs/index.html