The Ocelot (Cat) is new to minecraft and is only currently available to those using the weekly beta builds, and was available around 12w04a. You can get the latest beta weekly release directly from the mojang website. Creepers are especially scared of Ocelots and will avoid them by a 6-8 block radius, so if you have one following you Creepers should avoid you rather than sneaking up on you.
Ocelot's can be found roaming around in the new jungle boime areas.
Ocelots are quite wary creatures, and if you run at them or make any sudden movements they will sprint away from you. To taim have a raw fish in your hand and stand near the Ocelot. Wait for it to approach you and when it is close use the fish on it and it will become taimed. Once taimed it will follow you around, and if it falls too far behind you while traveling it will teleport to your location.