I want to catch Mew. I want to know what you need and where you need to..

To catch Mew you have to get an old sea map (nintendo event) and go to an island and he will hide from you but you can still catch him. To get to the upgraded safari zone, go up when you get in it untill you come to a big space, then you go east and you will be able to catch some new Pokemon there. Hope I helped.

You need a gameshark or an old sea chart to catch Mew, and the upgraded safari zone you need to beat the Pokemon leage.

For reasons I cannot tell you, I will answer this question in detail-LOL(is the game that serious or did I miss something?)
We ALL want to catch Mew, don't we, so no explaination needed there. Yes, Old Sea Map, Nintendo Event or maybe at the Nintendo HQ in NYC. Good freaking luck getting him that way! If he means enough to you, go spend $20 and get an Action Replay, go to the AR section of Emerald and find the Warp code(don't bother with the map!), and enter that, the master code, the dma disable, and start game. When you get to Faraway Island-just walk into any door to warp there-turn off the AR and follow Mew around in the grass until you bump into him and then battle him. That's the only way I can guarantee you can catch a Mew-and encounter codes work, too, but that's more fun!!
Safari Zone-once you're the champ-beat Elite 4 and rival-then a new area off to the right of the old area(guys are blocking off the entrance beforehand)and unique Jhoto Pokemon can be caught-different ones in the North area and the South area, so check both so you don't miss any.
BTW-the only thing you mispelled was cannot, don't be sorry, you're way better than most