Okay, how to make this all work. First thing you'll need is one copy of FaceBall 2000 for every Player, one compatible Game Boy for every player and one official Nintendo Game Boy Advance Link cable for every player. The official cables aren't too hard to find if you're willing to pay for 'em:

Okay, so you got the goods. The first step, put the 1 Game Pak into each Game Boy unit. Second, put the grey end of the Official Nintendo Game Boy Advance Link Cable into the link port on the first Game Boy you're using. If you're using an older Game Boy, the cable will require some unauthorized modification to fit the link port:

Now, grab another cable and plug the purple end of the first cable into the center box on the second cable:

Take the grey end of the second cable and plug it into the second Game Boy unit. Now, grab a third cable and plug the purple end of the second cable into the center box on the third cable - and plug the grey end of the third cable into the third Game Boy unit. Repeat this process for as many players as you plan to have. Once you reach the end, plug the purple end of the final cable into the center box of the very first cable - so you'll end up with a circle (or, in the case of this picture, a Triangle)...

Turn 'em all on and you should be ready to go.