All the DH customers can create promo codes and give discounts (max $97) to others.
When did you sign up? If you signed up recently, you should have 500GB space and 5TB bandwidth. If you signed up few months ago, you may not have it because DH has not started the new plan yet.
However, you can always check your plan via DH panel --> Billing --> Manage Account --> Hosting Plans If you like, you can also upgrade your current plan to happy plan with 500GB and 5TB.
Save $97 (MAX Discount) with code: [color=#CC0000]97YES[/color] [url=http://dreamhost.com/r.cgi?296804/signup|97YES]Sign Up NOW[/url] or More Codes Here