下面是JS脚本(floatdiv.js)
/*======================================================================
  浮动块支持脚本
  DESIGN BY :  彭国辉
  DATE:        2004-02-26
  SITE:        http://kacarton.yeah.net/
  BLOG:        http://blog.csdn.net/nhconch
  EMAIL:       kacarton@sohu.com

  文章为作者原创，转载前请先与本人联系，转载请注明文章出处、保留作者信息，谢谢支持！
======================================================================*/

var alLeft = 0, alCenter = 1, alRight  = 2;   //水平对齐方式
var alTop  = 0, alMiddle = 1, alBottom = 2;   //垂直对齐方式

var f = new Array();
var cnt = 0;

function floatDiv(objId, align, vAlign, x, y, smooth)
{
    /*浮动块对象
      数据结构：
        objId： 对象ID
        align： 水平对齐方式，枚举型
        vAlign：垂直对齐方式，枚举型内容
        x, y：  xy座标，整型
        smooth：平滑移动，布尔型
    */
    this.objId  = objId;
    this.align  = align;
    this.vAlign = vAlign;
    this.x = x;
    this.y = y;
    this.smooth = smooth;
}

function addDiv(objId, align, vAlign, x, y, smooth)
{   //添加浮动块
    f[cnt++] = new floatDiv(objId, align, vAlign, x, y, smooth);
}

function floatMove()
{   //重新定位各块位置
    var objX, objY;
    if (document.all)
    {
        var d = document.body;
//status = "scrollLeft:"+f[0].objId.style.pixelTop+"| offsetWidth:"+d.offsetWidth;
        for (var i=0; i<f.length; i++)
        {
            switch (f[i].align)
            {
                case alLeft  : objX = d.scrollLeft + f[i].x; break;
                case alCenter: objX = d.scrollLeft + Math.ceil((d.offsetWidth - f[i].objId.offsetWidth)/2) + f[i].x; break;
                case alRight : objX = d.scrollLeft + d.offsetWidth - f[i].x - f[i].objId.offsetWidth - 20; break; //减滚动条20
            }
            switch (f[i].vAlign)
            {
                case alTop   : objY = d.scrollTop + f[i].y; break;
                case alMiddle: objY = d.scrollTop + Math.ceil((d.offsetHeight - f[i].objId.offsetHeight)/2) + f[i].y; break;
                case alBottom: objY = d.scrollTop + d.offsetHeight - f[i].y - f[i].objId.offsetHeight; break;
            }
            if (f[i].smooth) smoothMove(f[i].objId, objX, objY);
            else
            {
                f[i].objId.style.pixelLeft = objX;
                f[i].objId.style.pixelTop  = objY;
            }
        }
    }
   
    if (document.layers)
    {
        for (var i=0; i<f.length; i++)
        {
            var objId = f[i].objId;
            switch (f[i].align)
            {
                case alLeft  : objX = pageXOffset + f[i].x; break;
                case alCenter: objX = pageXOffset + Math.ceil((window.innerWidth-objId.width)/2) + f[i].x; break;
                case alRight : objX = pageXOffset + window.innerWidth - f[i].x - document.objId.width; break;
            }
            switch (f[i].vAlign)
            {
                case alTop   : objY = pageYOffset + f[i].y; break;
                case alMiddle: objY = pageYOffset + Math.ceil(window.innerHeight/2) + f[i].y; break;
                case alBottom: objY = pageYOffset + window.innerHeight - f[i].y - document.objId.height; break;
            }
            if (t[i].smooth) smoothMove(f[i].objId, objX, objY);
            else
            {
                document.objId.left = objX;
                document.objId.top  = objY;
            }
        }
    }
   
    setTimeout("floatMove();",50);
}

function smoothMove(obj, x, y)
{
    var percent;
    if (document.all)
    {
        percent = .1 * (x - obj.style.pixelLeft);
        if (percent > 0) percent = Math.ceil(percent); else percent = Math.floor(percent);
        obj.style.pixelLeft += percent;
       
        percent = .1 * (y - obj.style.pixelTop);
        if (percent > 0) percent = Math.ceil(percent); else percent = Math.floor(percent);
        obj.style.pixelTop += percent;
    }
    if (document.layers)
    {
        percent = .1 * (x - document.objId.left);
        if (percent > 0) percent = Math.ceil(percent); else percent = Math.floor(percent);
        document.objId.left += percent;
       
        percent = .1 * (y - document.objId.top);
        if (percent > 0) percent = Math.ceil(percent); else percent = Math.floor(percent);
        document.objId.top += percent;
    }
}

setTimeout("floatMove();",50);

调用例子：

<script language="javascript" src="lib/floatdiv.js"></script>
<script language="javascript">
if (navigator.appName == "Netscape")
{
    document.write("<layer id=ad_hr top=300 width=100 height=120><a href=http://www.fpc.org.cn/hr/040522.htm target=_blank><img src='ad/hr40522.gif' width=120 height=180 border=0></a></layer>");
}
else
{
    document.write("<div id=ad_hr style='position: absolute;width:120;top:300;left:5;visibility: visible;z-index: 1'><a href=http://www.fpc.org.cn/hr/040522.htm target=_blank><img src='ad/hr40522.gif' width=120 height=180 border=0></a></div>");
}
addDiv(ad_hr, alRight, alTop, 0, 30, true);
</script>