Did an extensive bit of testing with this a while ago, I've got some docs from it somewhere. What to expect: Aside from the window focus, and the initial always out of sync problems which you can bypass (setting 1964 to auto go to full screen and forcing a connection interuption as soon as you start the game), they run at about 20fps on a 1.5mb/128kb cable connection, and 40fps on a 5mbs lan. After about 5 mins of gameplay time either way the games are unsyncable and kallaria disconnects from the server, meaning you get an error on the server, and the two games will keep playing as if the other player had stopped pressing buttons.
Basicly, its a good idea but for some reason with the n64 it doesn't work yet.
Your best bet is trying to play on a 10 or 100mbs lan.