I assume you're on a shared server (one of the regular packages that Dreamhost offers). That means your web site doesn't have a static IP address you can point to (unless you want to pay extra for the service).
Marsbar is right. You need to talk to your registrar and get them to unlock your domain so you can point to the DH nameservers or you'll need to get them to unlock it so you can transfer to another registrar who will let you use your property as you see fit. Good luck!