Ahhh, dial-up, the scourge of the netgamers...
Even with dial-up it should work, but, anyways...
1.start srb2
2.on the menu, select multiplayer
3.select host game
4.after finishing setting up the game (gametype, difficilty. etc.etc.)
5.select start game
6.wiat for people to join!
If you want to join an existing game...
On the left is console based, on the right is menu based.
1.open the console/or select multiplayer
2.type listserv and a list of servers will come up with there respective IP address/select join game (search)
3.type connect <ip address here>/select the game you want to join
4.hit enter!
that should work, sometimes the game will close saying that you need a certain .wad file, if the server has wad downloading on (default) and the MAXSEND is the same or higher than the size of the wad, you'll start downloading the wad into a folder called DOWNLOAD, you dont need to make the folder, its automatic.
Also, if your hosting a game, type listserv every now and then in the console, to see if your games still there, the master server sometimes bumps games off the list, do this if noone joins for a long time.
Also, you need to have the required UDP ports open, i dont know how to open these, but if it doesn't work, then its probably blocked by a firewall.
That should be all that you need to know.
Oh yeah, this is the best sonic game ever!!!
... i've wanted to say that for ages...