Since this is a fairly new feature, I don't think there's written instructiosn anywhere yet.
I'll do my best here. First you'll want to set up your domain and the database. These are both not accessable by your browser becuase DNS hasn't been updated yet.
In the same way that you can create a mirrored domain to access your site via http, we're going to create an other host name you can use to access the database.
Log into the panel > Goodies > Manage Mysql. Find your database and click the link "Hostname(s) for this MySQL server: [Add One]" Now add a host name like mysqlDomain.dreamhosters.com. You'll be able to use this to access phpmyadmin to upload your mysql database if it's smaller than 7mb.
What if your database is larger than 7mb? You'll have to fill the database through shell access, and if you're using shell access you don't need to add the dreamhosters host name. Your wordpress blog running on dreamhost will be able to access the hast name as if you had already transfered the DNS for your domain over. The server you're hosted on looks entries up in the DH DNS first, and then goes to an outside source if it doesn't find anything.
Does that make sense? You'll use the one click install of wordpress to put your install at example.com, with a hostname and database at mysql.example.com. Then set up a mirror of example.com at example.dreamhosters.com or somehting similiar. If you also want phpmyadmin access before you switch over your DNS, add an host name for your database at dreamhosters.com
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