Monster spawners do not (as of the version 1.3.1) ever contain creepers naturally. It is possible to get a spawner that spawns creepers by editing the game's code or by using mods.
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No, there are no creeper spawners naturally. Additionally, monster spawners will not spawn endermen or passive mobs (i.e. pigs, chickens, cows, etc.). You can although, download something such as not enough items, to obtain one.
Spawners are found in dungeons and mine shafts.
You can find iron ingots in chests next to monster spawners. But because monster spawners are rare then it would be a lot easier just to mine until you find some iron the melt it in a furnace! :)
Spawn a creeper egg and right click the ground. Or ./spawnmob creeper 100000
The creeper drops a music disc.