It's actually not as easy as it sounds, because we, as users, don't have access to the DH httpd.conf file - setting up apache exactly as DH has it is therefore difficult. Additionally, different DH servers have different apache modules loaded (and there are even different versions of apache running!). For more in formation about this, you might want to check this previous froum post about apache modules.
That said, you can come close to having the same environment if you set up your system as follows:
1) Determine what version of apache your domain is running, and use that.
2) Use the same, and only the same apache modules as your instance is running, particularly suexec.
3) Run a phpinfo() on your domain and determine the version number of PHP, and the php.ini contents, applicable, and duplicate them on your server.
4) Create a MySQL database via the Control Panel, and log into phpMyAdmin to determine the appropriate version number of MySQL you are running on Dreamhost (and other settings),and configure your MySQL instance the same way.
That ought to get you very close (I hope I have not left anything out ). On the other hand, you could just set up an "dev.yourdomain.tld" sub-domain, and develop there .