Welcome to DH!
The first thing you want to do may be to get familiar with DH's control panel. DH wiki is our great friend. You can find a lot of useful information over there.
You can view your files either via SSH or FTP. The easiest way is to use FTP via DH panel --> Domains --> Manage Domains --> WebFTP/FTP.
The files structure in DH is something like this: /home/username/domain.com All you files should be put into "domain.com" folder.
Be careful with WebFTP and FTP. If you use WebFTP, you will go into "domain.com" folder. If you use FTP, you will go to username folder and see three folders "Logs", "Maildir", and "Domain.com". Remember to put the files inside "Domain.com" folder.
No, you don't need to install yourself. They are already installed.
You can change PHP version of your domain via DH panel --> Domains --> Manage Domains --> Web Hosting --> Edit
According to DH's website on 19th of Jan, 2008, it is $3.95/mo
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