This is done by overiding the default styling of the GUI by declaring a new style at the end, eg. "..., "button");".
For example!
var toggleButton : boolean;
function OnGUI () {
//style toggle as a button!
toggleButton = GUI.Toggle (Rect (25, 25, 100, 30), toggleBool, "toggleButton", "button");
//style button as a toggle!
GUI.Button (Rect (10,140,180,20), "This is a button", "toggle");
}
You can read this in the GUI scripting guide, which is worth checking out for all the GUI references.
Neither of these work---- what the inquire is asking, is how does one switch on-off buttons and how does one extend this functionality to a consecutive series of buttons as the player clicks the buttons in the required sequence; just like a "regular" - event driven GUI we would find on all the current MMOs.
To date (06/13/2010) there has been no answer to this debacle for the UNITY 3D GUI system..