Hello. As the previous poster says, email caught by a DH catch-all address cannot be forwarded; but email caught by a "google apps" catch-all address can be; and dreamhost provides an easy way to arrange for all email addressed to a domain hosted at dreamhost to be handled by google apps.
There are probably many people here ready to give you step-by-step guidance, but I suggest you first look at
and confirm that this is the route you'd like to go.
The main issue that I'm aware of is that if you use google apps, you are the mercy of google's spam filter, which cannot be turned off and can only be trained to a limited extent.
P.S. some people have suggested ways of by-passing google's spam filter by using customizable filters, and other people have said this doesn't work reliably; if anyone has good information about that, please say!