function setObjectClass ( object, Class )
{
// Changes and objects class.
// Because you are only chnaging the class,
// the constructor will never be called.
//
// USAGE:
// setObjectClass ( myObject, myClass );

object.__proto__ = Class.prototype;
}

// SET CLASS BEFORE ATTACHING
registerLinkIDClass ( ‘box’, jgButton );
var box = this.attachMovie ( ‘box’, ‘box’, this.getNextHighestDepth() );

function registerLinkIDClass ( linkageID, Class )
{
// Associates a linkageID with a class.
// When you use attachMovie ( ‘linkageID’, … ),
// the movieClip will be an instance of that class.
//
// USAGE:
// registerLinkIDClass ( myMovieClipLinkageID, myClass );

Object.registerClass( linkageID, Class ); // register class to library linkageID
}

Function.prototype.cExtends = function(SuperClass)
{
this.prototype.__proto__ = SuperClass.prototype;
this.prototype.__constructor__ = SuperClass;
ASSetPropFlags(this.prototype, “__constructor__”, 1);

this.__proto__ = SuperClass;
}

SuperTest = function() {};
SuperTest.addStaticProperty(”prop”, 5);

Test = function() {};
Test.prototype = new SuperTest();

or
Test.cExtends(SuperTest);

Demonstration of object inheritance in Flash 5 ActionScript:
http://www.quantumwave.com/flash/inheritanceExample.html

Virtual Movieclip Class (aka MovieClip Inheritance or MovieClip SubClass)
http://www.quantumwave.com/flash/vmc.html

Demonstration of static methods and properties in ActionScript
http://www.quantumwave.com/flash/static.html

How to use Object.registerClass with 2.0 class
http://www.actionscript.org/forums/showthread.php3?t=37103&page=2

Multiple Inheritance
http://www.simonwacker.com/blog/archives/000007.php