On the fansite www.Armoredcoreonline.com they used to use a program called xLink Kai to play eachother from accross the world with the three latest PS2 games in the series.

If anybody has ACNX/ACNB/ACLR or likes the idea of playing this great series online then please post here and I can show you the steps to getting Armored Core hooked up with this program.

Armored Core Last Raven is the greatest game that I have ever played online and I just cannot get enough people to play against me at the right hours and I know that there are more gamers out there who fell in love with the series on ko4life.

xLink Kai
Hook two internet cords to your router (one for the comp, and another for the ps2)
Change your router settings and stuff (there are guides for each type of router, you only have to do this once.. ever)

Connect to the other player
play the game online