|The first thing to do is add each domain you'll be hosting with us to our system through the "Domains > Manage" panel, if it's not already listed on your account from the sign up process. Do this before you transfer your domain's dns to us! This won't screw up anything on the real Internet, but it will configure all our servers (mail, etc) as though your domain was here. You'll then have directories automatically created in your ftp users home directories for each domain... that's where you put the web files!
Then, in order to test your domains on our servers before you actually switch the dns, add free DreamHost (like say domain1.dreamhosters.com) sub-domains to your account (again through "Add Domain") and set them to "mirror" your actual domains you haven't switched over yet.
Then you'll be able to see what your sites will look like on our servers by going to http://domain1.dreamhosters.com/ on the web.
As for the email switchover, as long as you keep your old hosting account for a little while after you make the dns switch, you shouldn't lose anything. For a while, some emails will go to our servers and some will go to your old hosts.. but once the dns propagation is finished, all the email will be going to our servers and you can safely cancel the old account.
For databases, you can set them up here with a hostname at one of the dreamhost subdomains, and then you can remotely access them from your old host, or your new site here (or both). Once the transfer is done, you can actually just keep it at the dreamhost sub-domain forever if you want, or you can set up a second hostname (you can have two at a time) for it at your real domain, and then once that propogates you can remove the dreamhost sub-domain mysql host!
Last updated: Nov 22, 2005.