computers do not make IP's, routers and modems have them.
its not mac's fault, its not window's fault, its not the tutorial's fault.
even if you cant have a static IP, you still have an IP.
and forwarding would still work till you restart your computer or modem, and need to do so every annoying time.
if you couldn't get it to work even for the day before you shutdown, then you are the one still doing it wrong.