James,

please follow these steps:

• login to your original site as superuser ("host") and go to Portals in Host menu.
  Select your portal and add the domain address for the copy as additional portal alias.
  (preferably use same relative path, i.e. both in root or  in same virtual subdirectory)
• backup database and restore to a different database name
• make sure, database user has been granted same permission for the new database.
• create a new web site for the copy pointing to a new folder), and assign Host Header for the new domain address
• copy all files and subfolders from exisiting site to folder of the new site
• make sure, file system permissions have been granted properly for AS.Net account
• adopt web.config of the copied site to use copied database.
• browse your new site, enter "COPY" into the top module on home page and save
• browse to your original site and make sure, the copy doesnt get applied.
• you may also change background color of the copied site skin, to make it easy for you to distinct both sites.