How do you get different monster spawners on Minecraft 1.3.1?

Answer 1

Mob spawners generate naturally in dungeons, strongholds and abandoned mine-shafts. Dungeon spawners can be either; Zombie, Skeleton or Spider. Stronghold spawners will spawn only silverfish and mineshaft spawners spawn only cave Spiders. There are mods you can install to change what spawns in a spawner or to be able to pick a spawner up. You can also place spawners in creative mode, but they will only spawn pigs.

Answer 2

The only legitimate way to obtain a monster spawner in minecraft is with the /give command, so you must have cheats turned on in a world to get a monster spawner. Next, type /give (name of your player, or just 'player' if you're playing offline) 52 (amount of spawners you want to give yourself). Ta-da!

There are 2 conditions to this though: 1. It only works on the PC version (I think), and 2. The spawner(s) you will receive will only spawn pigs. You cannot get a spawner to spawn anything else unless you use a mod, such as the Too Many Items mod.

I'm sure others can expand on this, so feel free to add onto or correct what I've said!