The Code

function addHelp(target) {
  target.onRollOver = function( ) {
    // Delay the appearance of the help text by 1.2 seconds
    helpInterval = setInterval(createHelpText, 1200, target);
  };
  target.onRollOut = target.onDragOut=function ( ) {
    // Hide the help text when the user rolls off the clip
    clearInterval(helpInterval);
    removeHelpText( );
  };
}
function createHelpText(target) {
  // Create a clip to hold the help text
  var helpClip:MovieClip = attachMovie("helpText", "helpText", 
                          this.getNextHighestDepth( ));
  clearInterval(helpInterval);
  // Set the attributes of the help text
  var helpText:TextField = helpClip.helpText;
  helpText.background = true;
  helpText.backgroundColor = 0xFFFFCC;
  // Format the help text
  var helpFormat:TextFormat = new TextFormat( );
  helpFormat.leftMargin = 2;
  helpFormat.rightMargin = 2;
  helpFormat.indent = 0;
  helpFormat.size = 15;
  helpFormat.font = "_sans";
  // If the target has an accessibility name, 
  // display it in the help text box.
  if (target._accProps.name != undefined) {
    helpText.text = target._accProps.name;
  }
  if (target._accProps.shortcut != undefined) {
    // If the target has a keyboard shortcut, 
    // add it to the help text box.
    helpText.text += "\n" + target._accProps.shortcut;
  }
  // Set the help text's dimensions
  var fieldSize:Object = helpFormat.getTextExtent(helpText.text);
  helpText._height = fieldSize.textFieldHeight;
  helpText._width = fieldSize.textFieldWidth;
  helpClip._x = _xmouse - helpClip._width / 2;
  helpClip._y = _ymouse - helpClip._height - 10;
}
function removeHelpText( ) {
  helpText.removeMovieClip( );
}
function aHandler( ) {
  // Event handler for button A
  trace("You clicked A");
}
function bHandler( ) {
  // Event handler for button B
  trace("You clicked B");
}
function cHandler( ) {
  // Event handler for button C
  trace("You clicked C");
}
function down( ) {
  // Function to detect a key combo and 
  // run the associated button script.
  var allKeys;
  // Test to see if all the keys in the combo are down
  for (var j = 0; j < keys.length; j++) {
    allKeys = true;
    for (var i = 0; i < keys[j].combo.length; i++) {
      allKeys = allKeys && Key.isDown(keys[j].combo[i]);
    }
    if (allKeys) {
      // If all the keys in the combo are down, give the 
      // associated button focus, and run the associated
      // button's event handler. Finally, disable further 
      // events until the combo is released.
      Selection.setFocus(keys[j]);
      this.onKeyDown = undefined;
      this.onKeyUp = up;
      keys[j].btn.onRelease( );
      break;
    }
  }
}
function up( ) {
  // Function runs when a combo is released
  this.onKeyUp = undefined;
  this.onKeyDown = down;
}
//
var keys:Array = new Array( );
var keyListener:Object = new Object( );
keys[0] = {btn:buttonA, combo:[65]};
keys[1] = {btn:buttonB, combo:[Key.CONTROL, 66]};
keys[2] = {btn:buttonC, combo:[Key.CONTROL, 68]};
buttonA.onRelease = aHandler;
buttonB.onRelease = bHandler;
buttonC.onRelease = cHandler;
addHelp(buttonA);
addHelp(buttonB);
addHelp(buttonC);
keyListener.onKeyDown = down;
Key.addListener(keyListener);