Unfortunately you need to have *something*. Either the WordPress login details or the web hosting administration login details. The hosting owudl be better, but you can get by with only the WP ones. Unfortunately if you don't have those and you can't get in touch with the old developer it's going to be next to impossible to get access to the site. You could try contacting Dreamhost and see if they can help you. If you're the owner of the hosting account then they will do everything that they can. If the account is in the old developers name you might have a few problems, but they might still be able to work something out for you.