dont quote me on this but from what I have been reading,
For you to run a sizable game you would have to setup a PS2 dedicated Server.
What this means is you would have to download the software to your computer and install it. This would then allow you to host a game via your computer and connect to it via your PS2 and it should be listed so other PS2 players could connect to it.
If you are not running Cable or DSL I do not suggest setting up a server. The reason is that you are likly to see a lot of lag when you play the game.
Lag = Game Play Slow
I don't own a PS2 so I do not know if it has a built in server like the PC version kind of does. If it does and it is not just a LAN server then you should be good to go.
But if it is only a LAN server then for people to connect to it they would have to be on the same network as you. Meaning that they would have to be at your house.
I will see what else I can find and update this as soon as I see anything else.
Sorry I could not be more help
If you want here is the download for the PS2 Dedicated server
http://www.apocalypce.net/modules.php?name=Downloads&d_op=viewdownload&cid=5)