If you need to setup more than one company, you will need to set up a new subscription for each one. It means you will need to pay additional charges (NOT FREE) for setting up new subscription. They may offer some discount for adding new subscription.
You can use the same login name/ username for all the companies. When you log in you will get a list of the companies you have access to.
Simply go to http://quickbooks.intuit.com/
and sign up using the link “Already have an Intuit user ID?”