make sure you are running xlink 7.3, not 7.4: the last is told to be incompatible with ps3.
forward port 30000 of the computer that is running xlink kai.
once xlink is up and running, go to the cod black ops arena, ONLY THEN turn on your ps3, start cod black ops, go to multiplayer, lan, and if you don't see any hosts, host yourself a game.
after it starts, press select button, and you'll see who's connecting or connected to you.
PS3 Slim 500GB (bought right after JB was announced)
DIY PSGROOPIC, PS3Key, JailBreak clone