On how many PCs is my Norton Antivirus License valid for?

I purchased a boxed version of NAV which I *thought( was for only 1 PC however when I was in my account and I clicked purchase key, I saw this image:

 

 [IMG]http://i39.tinypic.com/anymhc.png[/IMG]

 

Does this mean that my license is also valid to be installed on 3 PCs?

 

Also, can one renew the subscription to add more validity to it or must I wait until my subscription is over?