Upgrade from P3, on a clean computer

I own P3, then did not use it since I installed Snow Leopard & reformatted everything and removed the bootcamp partition.

Now I want to buy P5 (since P3 upgrade support will end soon), and install it on my macbook, which do not have P3 installed anymore.

Can I? do I need to install P3 on it in order to "upgrade" ? But P3 will not install on Snow Leopard (I guess).

 

You save $30 when buying the upgrade. If you don't have Parallels Desktop 3 installed, then you need to enter both the old Parallels Desktop 3 permanent activation key and the Parallels Desktop 5 upgrade activation key.
http://www.parallels.com/products/desktop/whyswitch/howtoupgrade/