You can have up to 5 licensed devices - thats PC's, iPods, etc - that you authorise with your iTunes store log-in info. So All you'd have to do is buy it on one computer, then copy it across and enter your password on the new computer, then all purchases can be played on either computer
Ah fair play. In that case I have no idea! Try it and see? It'll ask you before you pay any money... so just test it and see how far it gets