Install a custom Launcher, unless you are talking about the physical buttons on some devices.
The launcher, like Launcher Pro, will allow you to display what functions and icons you wish. Generally, it will replace the stock launcher if you want it to. (there is an option to make it the default launcher) Make sure, whatever launcher you decide, doesn't require "root" access", or you will have to root your phone. Usually, it will tell you in the Market what the requirements are.