If the registration expired, I don't see how you could transfer it. If you let a domain expire that you care about, I'd try renewing it through your current registrar, then worry about the transfer later. Otherwise, you'd probably have to wait for it to drop and hope that someone else doesn't it grab it before you.
If you're able to renew it there, you'll probably have to wait 60 days before you can transfer it away anyway.
You don't have to register it here to host it here. If it's registered at Godaddy, or where ever, just set the nameservers to ns1.dreamhost.com, ns2.dreamhost.com and ns3.dreamhost.com.
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