可移动的Div（1）：MovableDiv
function MovableDiv(id) {
    this.obj = document.getElementById(id);

    this.obj.onmousedown = function() {
        if (event.srcElement != this) return;
        
        this._deltaX = event.x - this.offsetLeft;
        this._deltaY = event.y - this.offsetTop;
        this._dragging = true;
        this.setCapture();
    };

    this.obj.onmousemove = function() {
        if (this._dragging) {
            var x = event.x - this._deltaX;
            x = x < 0 ? 0 : x;
            var y = event.y - this._deltaY;
            y = y < 0 ? 0 : y;
            this.style.left = x + "px";
            this.style.top = y + "px";
        }
    };

    this.obj.onmouseup = function() {
        this._dragging = false;
        this.releaseCapture();
    };
}

可移动的Div（2）：WidgetContainer
Type.registerNamespace("Monster");

Monster.WidgetContainer = function(element) {
    Monster.WidgetContainer.initializeBase(this, [element]);
    
    this._mouseDownDelegate = null;
    this._mouseMoveDelegate = null;
    this._mouseUpDelegate = null;
    this._dragging = false;
    this._deltaX = 0;
    this._deltaY = 0;
}

Monster.WidgetContainer.prototype = {

    initialize: function() {
        if (this._mouseDownDelegate === null) {
            this._mouseDownDelegate = Function.createDelegate(this, this._mouseDownHandler);
        }
        $addHandler(this.get_element(), "mousedown", this._mouseDownDelegate);

        if (this._mouseMoveDelegate === null) {
            this._mouseMoveDelegate = Function.createDelegate(this, this._mouseMoveHandler);
        }
        $addHandler(this.get_element(), "mousemove", this._mouseMoveDelegate);
        
        if (this._mouseUpDelegate === null) {
            this._mouseUpDelegate = Function.createDelegate(this, this._mouseUpHandler);
        }
        $addHandler(this.get_element(), "mouseup", this._mouseUpDelegate);
                
        Monster.WidgetContainer.callBaseMethod(this, "initialize");
    },
    
    dispose: function() {
        if (this._mouseDownDelegate) {
            $removeHandler(this.get_element(), "mousedown", this._mouseDownDelegate);
            delete this._moseDownDelegate;
        }
        
        if (this._mouseMoveDelegate) {
            $removeHandler(this.get_element(), "mousemove", this._mouseMoveDelegate);
            delete this._mouseMoveDelegate;
        }
        
        if (this._mouseUpDelegate) {
            $removeHandler(this.get_element(), "mouseup", this._mouseUpDelegate);
            delete this._mouseUpDelegate;
        }
        
        Monster.WidgetContainer.callBaseMethod(this, "dispose");
    },
    
    _mouseDownHandler: function(e) {
        this._dragging = true;
        this._deltaX = e.offsetX;
        this._deltaY = e.offsetY;
        this.get_element().setCapture();
    },
    
    _mouseMoveHandler: function(e) {
        if (!this._dragging) return;
        
        var left = this.get_element().offsetLeft + e.offsetX - this._deltaX;
        left = left < 0 ? 0 : left;
        var top = this.get_element().offsetTop + e.offsetY - this._deltaY;
        top = top < 0 ? 0 : top;
        Sys.UI.DomElement.setLocation(this.get_element(), left, top);
    },

    _mouseUpHandler: function(e) {
        if (this._dragging) {
            this._dragging = false;
            this.get_element().releaseCapture();
        }
    }
}

Monster.WidgetContainer.registerClass("Monster.WidgetContainer", Sys.UI.Control);

if (typeof(Sys) != "undefined") Sys.Application.notifyScriptLoaded();

创建WidgetContainer
<script type="text/javascript" language="javascript">
    function pageLoad(sender, args) {
        $create(Monster.WidgetContainer, { }, { }, null, $get("div1"));
    }
</script>