If you're trying to understand multiplayer, cable modems and all the rest,
don't go to GP3 for your explanation. That is a bad model, as the process
of trying to play online and all you have to go through to get it not to
work, is too convoluted.
You do need a TCP/IP protocol installed to play using a cable modem. That's
for any game that has TCP/IP support. But it's very unlikely that you'll be
able to play GP3 over the net. I've tried it before-- only briefly-- and it
was so slow that I gave up even thinking that the game had a chance of
having decent online play. Playing the game at home on a LAN is possible
and works pretty well, despite, again, having to go through some unorthodox
procedures to get it to work.
Alanb