I agree with quigy if you are beginner you don�t have to care how much to invest, just try a couple of times, few months and you�ll be ready for more real life. Also if you are not a newbie, you can try with micro or mini accounts. Most brokers offer very small �mini-accounts� and even smaller "micro-account" for as little as a couple hundred bucks. Anyway be careful!
I think what you have said is true, but I feel he just want to know the margins from all traders here to see what to start with.