Lets clear things up a bit: what do you want to do exactly?
You want to hide the fact you online from your lan admin or from an admin of a server u use on the internet?
If the first case, u most likely cant do that. You can block ping messages, and incomming lan connections except the gateway, but if the switch is an advanced one, the admin simply log into it, and chack it, who is online, or simply check the leds, if its near him.
In case if you want to hide your ip on the internet, well there are methods to do this, tell more precisely what do you want to do.