New domain same site?

I’ve just registered a new domain name (through DreamHost) which I would now like to point to an existing site (hosted by Dreamhost).

How should I do this?

Is the existing site hosted in your account or elsewhere?

Hosting and domain reg both by DreamHost.

I’ve set a redirect on the domain for now, but I’d rather replace it.

If I am not mistaken, you are looking for mirror domain

Right you are. I got there in this thread over here