It sounds as though you may have only registered the new domain at Dreamhost, and have not yet "hosted" it. Once you have a domain (whether or not Dreamhost is the registrar), you have to "Add a Domain" via the Manage Domains section of the Dreamhost Control Panel
The process of registering and adding hosting can be a "two-step" process, as Dreamhost lets you host domains that you have not registered at Dreamhost.
You can host as many domains as you want on Dreamhost plans, without extra charges, and it doesn't matter where the domain is registered.
Just go to the link I provided above, and "add" the new domain (that you registered at Dreamhost) and it will then show up in your panel. Good Luck!