Okay, so, I've been trying to do this for a few days now, but it isn't working. I've followed various "How To's" and still nothing.
Here's what I've done;
I've downloaded Forge and ran it's profile on Minecraft.
I've copied the Mo'Creatures and Custom Mob Spawner zips into my.minecraft/mods folder.
Now, Forge runs fine. But it doesn't seem to want to add the others to my game.