如何拖动层

下面是一个完整的HTML文档
＜HTML＞
＜head＞
＜script＞
var down = false;
function UpMouse(){
down = false;
}
var startX = 0; startY = 0;startLeft = 0;startTop = 0;
function MoveLayer(){
if (down){
thelayer.style.pixelLeft = startLeft+event.clientX-startX;
thelayer.style.pixelTop = startTop+event.clientY-startY;
formview.viewpos.value = " X:"+event.clientX+" Y:"+event.clientY+"
startX:"+startX+" startY:"+startY;
}//可以观察鼠标的运动
}
function DownMouse(){
if (!document.all) return true;//暂时只支持4.0以上的IE浏览器
if (event.srcElement.name=="layermove"){//对应要拖动的层的name
thelayer = event.srcElement;
down = true;
startX = event.clientX;
startY = event.clientY;
startLeft = thelayer.style.pixelLeft;
startTop = thelayer.style.pixelTop;
}
}
＜/script＞
＜/head＞
＜body onmousedown="DownMouse()" onmousemove="MoveLayer()" onmouseup="U
pMouse()"＞
＜form name="formview"＞
＜center＞
＜input name="viewpos" value="　这里显示鼠标的运动轨迹" size="37" style
="border=0;color:white;background:blue"＞
＜/center＞＜!--隐藏了文本框的边框，这也算是一个DHTML的应用吧。呵呵！--＞
＜/form＞
＜div name="layermove" style="position:absolute;top:100pt;left:215pt;cu
rsor:hand;background:#f5f5ff;width:150pt;height:100pt"＞
＜p align="center"＞

这个层可以拖动？！

不信你试试看！＜/p＞
＜/div＞
＜/body＞
＜/HTML＞