from the dreamhost admin:
"Note, even if you host a domain with us, if you registered it elsewhere, you must go there to renew or modify registration info."

from my 1and1 account, I can do:
choose domains
select the domain (checkbox) and choose dns from the top
edit "Name Server Settings"
change the IP address to the dreamhost address
optionally change the mail record (MX) to the dreamhost server.

this may need corresponding config on dreamhost's side though