Yes I've done it on my second older PC. I had to register it over the net and it was accepted automatically but,my second PC has an identical set up. That is to say, the same motherboard, same software, same memory but slightly less.
You should be aware that the pricipal of registration is to stop pirating and as far as I am aware, my set up does pass muster. Apart from that I certainly would NOT entertain passing the PC on to another person with the operating system loaded.
If you are in a position to do a bit of pirating then don't do it.