Multiplayer is LAN only, internet play is not really supported in gp3, some code was written in but it's pretty useless. It is possible with gpx_patch, but extremely difficult and due to data transfer problems it can take up to 5 minutes for the lights to go green and another 5 minutes to get to the first chicane at Monza ;-/ This is a hot topic in the Forum Archiv, well worth a look. Good luck with it.
[
www.mediafire.com] Some say you should click it, you know you want to.
[
www.gp4central.com] <----GP4 Central