1 license = 1 computer at a time. If you have 5 boxes (that you intend to play all at once) you need 5 licenses.

If you intend to do 1 at a time = then you need to contact the dev and have him update your license everytime you change your PC.

Lots of other options out there if you actually have multiple boxes and don't want to pay x5 - HKN works well, lavishsoft is good, Octopus, etc.