it's a tremolo! what sustain? :p just kidding

here's how you get it so it doesn't vibrate against the body, don't tighten the springs so much that the bridge is touching the body! the idea is to have the screws in just far enough to be equal with the tension of the strings. so that the strings are pulling the bridge one way, while the springs bring it back the other way, you want to set it up so that the springs provide an equal tension to the strings, so that the bridge is "floating" level with the body.

the block of wood idea is just wedging in a block of wood between the trem and the body so that the bridge cannot move from it's "floating" position, even if you took the springs off. because then the strings are tugging on the bridge, which is held in place by the block of wood.. therefore, it's goin nowhere!

hope this helps you to better understand