At least on Tiger, if you simply mute the sound before you power off, you will not get the start up chime when you next power up. Of course at that point, you have no sound at all until you re-enable it.
Most people LIKE the start up chime. It is part of the charm of a Mac! I am guessing that you are new to the world of Macs? Give it a bit of time. I am hopeful that you will come to like it too.
I have to disagree with you. It doesn't have anything to do with getting used to it. There's situations where you don't want to have a loud startup chime, like in the library, in class or when someone's sleeping and you need to use your computer. I've been a mac user my whole life and I can go without the chime at times. It's nice to be able to have that option without having to set the volume manually to silent before shutting down, so that the chime doesn't come on at the next startup.
You have a laptop, why do you need to shut it down?
You can stop the startup sound using tinkertool amongst other utilities My machine does not reset the volume to halfway so I can't help you with that.