怎样在web上建立一个可以拖动的层（或者其它可以拖动的东西）

<HTML>
<HEAD>
<META content="text/html; charset=gb2312" http-equiv=Content-Type>
<STYLE>
#floater {CURSOR: move; POSITION: absolute; RIGHT: 40px; TOP: 70px; Z-INDEX: 3}
</STYLE>
</HEAD>
<BODY>
<TABLE bgColor=white border=2 cellPadding=0 cellSpacing=0 id=floater>
<TR>
<TD>
文字，表格等<br>
文字，表格等<br>
文字，表格等<br>
文字，表格等<br>
文字，表格等<br>
</TD>
</TR></TABLE>
<SCRIPT>
function grabIt(e) {
whichIt = event.srcElement;
while (whichIt.id.indexOf("floater") == -1) {
whichIt = whichIt.parentElement;
if (whichIt == null) { return true; }}
whichIt.style.pixelLeft = whichIt.offsetLeft;
whichIt.style.pixelTop = whichIt.offsetTop;
currentX = (event.clientX + document.body.scrollLeft);
currentY = (event.clientY + document.body.scrollTop);
return true;}function moveIt(e) {
if (whichIt == null) { return false; }
newX = (event.clientX + document.body.scrollLeft);
newY = (event.clientY + document.body.scrollTop);
distanceX = (newX - currentX); distanceY = (newY - currentY); currentX = newX; currentY = newY;
whichIt.style.pixelLeft += distanceX; whichIt.style.pixelTop += distanceY;
if(whichIt.style.pixelTop < document.body.scrollTop) whichIt.style.pixelTop = document.body.scrollTop;
if(whichIt.style.pixelLeft < document.body.scrollLeft) whichIt.style.pixelLeft = document.body.scrollLeft;
if(whichIt.style.pixelLeft > document.body.offsetWidth - document.body.scrollLeft - whichIt.style.pixelWidth - 20) whichIt.style.pixelLeft = document.body.offsetWidth - whichIt.style.pixelWidth - 20;
if(whichIt.style.pixelTop > document.body.offsetHeight + document.body.scrollTop - whichIt.style.pixelHeight - 5) whichIt.style.pixelTop = document.body.offsetHeight + document.body.scrollTop - whichIt.style.pixelHeight - 5;
event.returnValue = false;
return false;}function dropIt() {whichIt = null;return true;}function heartBeat() {
diffY=document.body.scrollTop;diffX=document.body.scrollLeft;
if (diffY!=lastScrollY) {
percent=.1*(diffY-lastScrollY);
if (percent>0) percent=Math.ceil(percent);else percent=Math.floor(percent);
document.all.floater.style.pixelTop += percent;
lastScrollY = lastScrollY + percent;}
if (diffX!=lastScrollX) {
percent=.1*(diffX-lastScrollX);
if (percent>0) percent=Math.ceil(percent);else percent=Math.floor(percent);
document.all.floater.style.pixelLeft += percent;
lastScrollX=lastScrollX + percent;}}self.onError=null;
currentX = currentY = 0;
whichIt = null;
lastScrollX = 0; lastScrollY = 0;
document.onmousedown = grabIt;
document.onmousemove = moveIt;
document.onmouseup = dropIt;
action = window.setInterval("heartBeat()",1);
</SCRIPT>
</body></html>