No, not without cheating.
The only way, I repeat, the ONLY way to get Jirachi on Sapphire without cheating is to connect your Sapphire game to the bonus disc included with pre-ordered copies of Pokemon Colosseum. Good luck finding it on eBay!
No, Jirachi is only available by Nintendo events or by cheating.
you dont
No, you cannot catch a mew in Pokemon Platinum without cheating.
yes you can catch it with anything
you can get jirachi on Pokemon Channel a GameCube Game at the end of the game you'll get jirachi
you cant catch a jirachi
No you cannot.
In emerald you can catch deoxys and jirachi but your internal battery needs to be working if it is keep going to the space center until they get to rocket launch 99 then talk to the dude that tells you which one there on and he'll ask if you would want to go on 100 if you do you can catch jirachi and deoxys if not you can catch celebi the same goes for ruby and sapphire hope this helps
Cheating
you cant catch them without cheating and cheating is bad! dont do that cheating thing man; its bad man