Aha! I just missed that line in my first response, so I have another possible (probable) solution for your issue.
Remember that registration and hosting are two different things! As they remind you when a new registration is completed, the act of registering a domain does not “automagically” arrange for it’s hosting, and hosting is required for email, site set-up, db access, one-clicks, etc. - in fact for everything other than registrations itself. If you did not do this, here is how you do it:
Go to the Control Panel -> Domains -> Manage Domains screen and select “Add a Domain or subdomain”, and add the domain you just successfully registered. Complete and submit the form, and wait till you get the email indicating the domain is now hosted or you see the little “clock” icon is no longer next to the domain name when you visit the Control Panel -> Domains -> Manage Domains screen.
Once that has happened, you may now upload you site, create email addresses for users, database, one-clicks ( installations, etc. You will still have to wait until DNS for the new domain has updated across the web to visit the site in your browser. This can take from a few minutes to several days, will vary from person to person and computer to computer, and you can’t really speed it up - just be patient.
If you really need or want to see the domain before the DNS is updated, you can follow the procedure described int this DreamHost Wiki article on viewing your site before DNS change is complete.