Actually, this topic belongs at this board: N64 and Gamecube
. Anything that has to do with N64 or Gamecube Pokemon games belongs there.
There is already a help thread at this location: Pokemon Colosseum Help Thread
. Just go to that location, ask your question and I'm sure someone would help you (though I believe your friend needs his own GBA and link cable, but I'm not 100% sure).