OS X 10.5.8 Licensing?

I'm a newbie to Mac, so sorry if this is a dumb question. With Windows, if I buy a used copy of Windows 7 for a machine that came with Windows XP and the previous owner is already using the license key; I'm not going to be able to successfully register and run the installation I installed from that disc.

So if I buy a used copy of OS X Leopard from someone, is it going to require any kind of license key?