There are a couple different ways to do it- 1.) mod your ps2 hardware or 2.) use a cd/dvd thing that you insert before putting in your import game. I've done this a lot with the PS1 and GameCube, and I HIGHLY recommend the second option. It's a lot easier and less of a headache if you mess up.
Here's a PS2 cd import loader thing (first product in the list):
http://www.smashbros.com/en_us/gamemode/wi-fi/wi-fi01.html You can also battle with people you donít know who are looking for brawls. The most important point here is that you will not know each otherís names.