You can buy the OS from Apple, but to install it, you need to use hacked drivers and the like - it's certainly no felony but using those hacked drivers does open you up to the possibility of facing a civil lawsuit. There's some on the net who claim that they've gotten AMDs to run Leopard, but to be honest, just get Ubuntu or another linux that's out there, and enjoy it that way. Or pick up a Mac Mini or MacBook for cheap and explore on those.
I checked, and you are probably correct about that - although there may be some circumstances like distributing it on-line or installing more than ten copies that could rise to that level. I agree with the alternatives you recommend.