请教关于层的浮动的问题！


<head><meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta name="GENERATOR" content="Microsoft FrontPage 4.0"><meta name="ProgId" content="FrontPage.Editor.Document"><title>跟随屏幕移动的图像</title><style type="text/css">#L1 {position: absolute;left:105px; top:-1px; width: 738px; height: 125px;visibility: visible;z-index: 10;}</style></head><body><div ID="L1" style="left: 490px; top: 158px">
<p align="center"><img SRC="csdn.gif" alt="图片显示的文字" WIDTH="225" HEIGHT="160"><br></p>
<table width="223"><tr><td bgcolor="#E2F5FF" height=1000 width="217"></td></tr></table></div><script LANGUAGE="JavaScript">
<!--self.onError=null;currentX = currentY = 0;whichIt = null;lastScrollX = 0; lastScrollY = 0;NS = (document.layers) ? 1 : 0;IE = (document.all) ? 1: 0;<!-- STALKER CODE -->function heartBeat() {if(IE) { diffY = document.body.scrollTop; diffX = document.body.scrollLeft; }if(NS) { diffY = self.pageYOffset; diffX = self.pageXOffset; }if(diffY != lastScrollY) {percent = .1 * (diffY - lastScrollY);if(percent > 0) percent = Math.ceil(percent);else percent = Math.floor(percent);if(IE) document.all.floater.style.pixelTop += percent;if(NS) document.floater.top += percent; lastScrollY = lastScrollY + percent;}if(diffX != lastScrollX) {percent = .1 * (diffX - lastScrollX);if(percent > 0) percent = Math.ceil(percent);else percent = Math.floor(percent);if(IE) document.all.floater.style.pixelLeft += percent;if(NS) document.floater.left += percent;lastScrollX = lastScrollX + percent;}}<!-- /STALKER CODE --><!-- DRAG DROP CODE -->function checkFocus(x,y) { stalkerx = document.floater.pageX;stalkery = document.floater.pageY;stalkerwidth = document.floater.clip.width;stalkerheight = document.floater.clip.height;if( (x > stalkerx && x < (stalkerx+stalkerwidth)) && (y > stalkery && y < (stalkery+stalkerheight))) return true;else return false;}
function moveIt(e) {if (whichIt == null) { return false; }if(IE) {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;} else { whichIt.moveTo(e.pageX-StalkerTouchedX,e.pageY-StalkerTouchedY);if(whichIt.left < 0+self.pageXOffset) whichIt.left = 0+self.pageXOffset;if(whichIt.top < 0+self.pageYOffset) whichIt.top = 0+self.pageYOffset;if( (whichIt.left + whichIt.clip.width)>= (window.innerWidth+self.pageXOffset-17)) whichIt.left = ((window.innerWidth+self.pageXOffset)-whichIt.clip.width)-17;if( (whichIt.top + whichIt.clip.height) >= (window.innerHeight+self.pageYOffset-17)) whichIt.top = ((window.innerHeight+self.pageYOffset)-whichIt.clip.height)-17;return false;}return false;}function dropIt() {whichIt = null;if(NS) window.releaseEvents (Event.MOUSEMOVE);return true;}<!-- DRAG DROP CODE -->if(NS) {window.captureEvents(Event.MOUSEUP|Event.MOUSEDOWN);
window.onmousemove = moveIt;window.onmouseup = dropIt;}if(IE) {
document.onmousemove = moveIt;document.onmouseup = dropIt;}if(NS || IE) action = window.setInterval("heartBeat()",1);// -->
</script></body></html>