Log into the panel and go tot his page: https://panel.dreamhost.com/index.cgi?tree=domain.registration&
If it’s expired, renew it…
If not check this page: to see if your past due: https://panel.dreamhost.com/index.cgi?tree=billing.payment&
if not open a support ticket with this page: https://panel.dreamhost.com/index.cgi?tree=support.msg&
and if for some reason you are locked out of the panel then you will have to use this generic contact form: http://dreamhost.com/contact/ but that should be your last resort.
Also if by “but Dreamhost still seems to own it. I can’t re-register, or renew.” means that you intentionally let it expire so that you could renew it elsewhere, that won’t work… First there is a 30 day grace period, then there is a redemption period, then there is more time… then the domain finally goes back up for grab… it’s about a 6 month delay usually.
If you are trying to move it elsewhere then register it at dreamhost, change the nameservers to your new host to get you back in business, and then when you can do a domain transfer to transfer the registration, or you can just keep dreamhost as your registrar and leave the nameservers pointed elsewhere.