Here's a hint - DH is "Shared" hosting which means that none of us have "root" on these machines. We share it with 100 or so of our dearest friends that we never see but complain about all the time.
All of the "basics" - Apache, mysql, php and many many other things are already ready to go on your server. Look around through the control panel and the wiki (http://wiki.dreamhost.com) before doing anything drastic and ask on the forums here and maybe we can save you lots of effort!
Wholly - Use promo code WhollyMindless for discount.