Autodesk has finally released the latest versions of Revit. You probably already know this, unless you've been without Internet access.
Revit Architecture 2008 is available for download HERE.
Revit Structure 2008 is available for download HERE.
Revit MEP 2008 is available for download HERE.
If you have difficulty with authorization you can try logging into the Registration site directly. Run Revit and attempt to register first. It will generate a request code, displayed at the top of the form.
Then visit the Registration site and login. If you've never done it this way before you'll need to setup your account. Once you are logged in you need to choose the account, if you have more than one you are responsible for, and provide the product serial number. Next you'll be asked for the request code and finally you'll get the activation code to enter into the registration form in Revit. This code is pasted into the form generated while using Revit. The activation code is also emailed to the email address for your account.
I needed to do this to get the authorization so you might too.