How is it possible to use domain/server space bought from one vendor with a domain name registered under another?

Transferring your domain to a new Web Host means pointing your Domain Name System (DNS) to a name server that supports name-to-address translation. (Your Web Host should be able to help you with this.) It usually takes anywhere from 2 to 4 days before the process is completed. During this time, your website will be sitting on two servers—your old ISP's and your new ISP's. To know when the DNS has propagated, I recommend making a small modification to your home page (e.g., change the mouse over color of your links). This way, you will know when it's safe to cancel your old Web hosting service.