Domain's don't work that way. You first register the domain at Answerable. Then you find the URLs of the name servers of ipbhost. You set your domain to point to those name servers. Now, if IPB also supports full domain management, you should be able to set it up there so that it uses your domain. If not, you will only be able to set it up so it masks your site with the domain. While CP was with invisionfree over 3 years ago I was only able to turn on masking, full domain redirection was not supported. :/ If you are paying for your forum, though, you should be able to able to have full redirection control.