Normally, if your domain name was registered some place other than DreamHost, it would be a simple matter of setting the name servers for the domain to point at the DreamHost name servers, then having your friend add the domain to the DreamHost hosting system as 'fully hosted' via the panel at Domains -> Manage Domains -> Add New Domain / Sub-Domain.
However, I am not sure this procedure will work if the domain is registered under another DreamHost account, but it's definitely worth a try.
First, set the name servers for your domain by going to Domains -> Registrations in the panel, ticking the whois box for your domain, then clicking the Modify whois for selected... link. At the bottom of the resulting page you will see the section for setting the name servers, set them to...
Once this has been done, have your friend add your domain via his panel (as detailed above). If all goes well, the domain should be up and working once the new DNS information propagates around the Internet.
As I said, I am not sure whether this procedure will work when the domain is registered under another DreamHost account. If not, then I believe you will have to contact DreamHost support and have them 'move' the domain to your friends account.
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