There is an option to turn off all of the monsters by setting the difficulty to 'Peaceful' and I'm sure there's some invulnerability mod to not let you die outside of creative.
I haven't touched Minecraft in almost two years to be honest. I used to play it quite a lot, but I burnt out badly by the time Beta 1.6 came out. Now I can't even touch the game no matter how modded it is. My friend has been pushing me to play Tekkit with him though.