If you mean you can not access it by FTP, then that means it was installed with the Simple Installation and then you will not get access any way.
You need a custom install for backend FTP access.
As far as I know the only thing you can do is make a backup with Xcloner plugin and then delete the current WordPress installation. Install it again with Custom Install option and use the restore option from XCloner.
Maybe this will cause problem, since I am sure Dreamhost adds something when did the Simple Install.
So basicly I think you will either start all new or deal with the inheritence you got.
Sorry no good news for this problem