I’m not sure I follow – did you register the domain with Yahoo, or with DreamHost, or with something like GoDaddy?
And where are you hosting the site? I.e., what server are the actual files sitting on?
Generally you won’t be tinkering with your actual DNS entry – you just assign the proper nameservers with your registrar, and your host handles the IP address details.
For example, if you registered the domain name with DreamHost, but you are hosting the site with Yahoo, you’d check with Yahoo what nameservers you’re supposed to use (probably something like ns1.yahoo.com, ns2.yahoo.com, etc.), then go to http://panel.dreamhost.com and click on Domains --> Registrations, hit the Modify button for the domain, and enter the name servers there. That’s all you need to do.