You mean you want to host his domain here at DreamHost, while leaving the actual domain name registered elsewhere?
If so, then your friend needs to use whatever configuration tools are provided by his domain registrar to change the name servers for his domain to...
Now, you need to add his domain to the DreamHost system via the admin panel at Domains -> Manage Domains -> Add New Domain / Sub-Domain, you need to add the domain as Fully Hosted.
Once these steps have been taken it will take sometime for the new DNS information to propagate across the Internet, up to 72 hours in some cases.
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