well... you have to get an r4 or any sort of cheat card to do that. you can not do it on the normal game card.
you can't
You can't steal Pokemon however in Pokemon colosseum and Pokemon xd gale of darkness you can snag shadow Pokemon from trainers.
Pokemon black has exclusive Pokemon and an exclusive location called black city where you can battle trainers with high leveled Pokemon and you can catch reshiram, while for white version it has more exclusive Pokemon, a exclusive area called white forest where you can catch lower leveled Pokemon of the trainer's Pokemon and you can catch zekrom.
This is the code for "Catch Trainers Pokemon" B6C5368A 08BE8FF4 B8D95CFE 06ED6EA1 E151C402 8A229A83 8E883EFF 92E9660D Press L+R in battle to be able to catch trainers pokemons as if they were wild.
only if you have the catch trainers Pokemon code
You cant catch any trainers Pokemon
you dont
no
Seriously? You can't catch trainers.
You can't catch or obtain other trainers Pokemon in emerald.
battle trainers or catch the Pokemon
No. You can only battle trainers and receive special items after battling a certain number.