特点：
1、兼容 IE6、FF、Opear（IE7还没有机会测试）
2、拖动流畅
3、起点与终点之间有过渡，使移动更平滑(可调)

演示

/*
    Author:misshjn
    HomePage:http://www.happyshow.org
    Date:2007-04-30

    拖动开始
*/
function _getStyle(element,styleProp){
    if (element.currentStyle){
        var y = element.currentStyle[styleProp];
    }else if (window.getComputedStyle){
        var y = document.defaultView.getComputedStyle(element,null).getPropertyValue(styleProp.replace(/([A-Z])/g,"-$1").toLowerCase());
    }
    return y;
}
function _elementOnmouseDown(evt,blockID){
    var obj, temp;
    obj=document.getElementById(blockID);
    var x = evt.clientX || evt.pageX;
    var y = evt.clientY || evt.pageY;
    obj.startX=x-obj.offsetLeft;
    obj.startY=y-obj.offsetTop;

    var d = document.createElement("div");
    d.style.position = "absolute";
    d.style.width = obj.clientWidth + parseInt(_getStyle(obj,"borderLeftWidth"),10) + parseInt(_getStyle(obj,"borderRightWidth")) -2 + "px";
    d.style.height = obj.clientHeight + parseInt(_getStyle(obj,"borderTopWidth"),10) + parseInt(_getStyle(obj,"borderBottomWidth")) -2 + "px";
    d.style.border = "1px dashed #666";
    d.style.top = _getStyle(obj,"top");
    d.style.left = _getStyle(obj,"left");
    d.style.zIndex = "9999";
    document.body.appendChild(d);
    document.onmousemove=function(evt){
        d.style.left= (evt?evt.pageX:event.clientX) - obj.startX + "px";
        d.style.top= (evt?evt.pageY:event.clientY) - obj.startY + "px";
    };
    document.onmouseup=function(){
        var objL = parseInt(_getStyle(obj,"left"),10);
        var objT = parseInt(_getStyle(obj,"top"),10);
        var obj2L = parseInt(d.style.left,10);
        var obj2T = parseInt(d.style.top,10);

        var todolist = [];
        var level = 10;  //元素移动从起点到终点之间过渡的级数,大于0的整数
        var speed = 10; //毫秒，每次移动的间隔时间，数字越大，动画感越强，但跳跃感也越大
        for (i=1; i<=level; i++){
            todolist.push(function(t){
                setTimeout(function(){
                    obj.style.left = objL + (obj2L-objL)*(t/level) + "px";
                    obj.style.top = objT + (obj2T-objT)*(t/level) + "px";
                    if(t==i)todolist=null;
                },speed*arguments[0]);
            });
        }
        for (i=1; i<=level; i++){
            todolist[i-1](i);
        }
        document.body.removeChild(d);
        document.onmousemove = null;
        document.onmouseup = null;
    };
}

/*
    拖动结束
*/