On-screen button press

How would I place a small GUI button on the screen in the top right corner and script for what to do when you click it? Also, what program would you recommend that I use to draw this GUI graphic.

void Update() {
   if (GUI.Button(new Rect(Screen.width / 4 * 3, Screen.height / 4, 25, 10), "Example Text")) {
      // The button has been clicked

This creates a standard GUI Button at 75% screen width, 25% screen height, 25 pixels wide, 10 pixels high.

Also check out http://unity3d.com/support/documentation/ScriptReference/GUI.Button.html