<script language="JavaScript">
function iniCopos(num, anc, alto, veloc)
{
var i, x, y;
for (i = 0; i<num; i++)
    {
    x = parseInt(Math.random()*anc);
    y = parseInt(Math.random()*alto);
    dibujaCopo(i,x,y);
    }
window.copos = new Array(num);
window.coposAlto = alto;
window.coposAncho = anc;
window.coposVeloc = veloc;
}

function dibujaCopo(num, x, y)
{
var tama = Math.round(Math.random())+ 3
document.write('<div id="c'+num+'" style="position:absolute; width:1px;');
document.write('height:1px; z-index:0; left:'+x+'px; top:'+y+'px; ');
document.write(' background-color: #FFFFFF">');
document.write('<font size="+'+tama+'" color = "#FFFFFF" >*</font>');
document.write('</div>');
}
function iniNevada()
{
for (i = 0; i < window.copos.length; i++)
if (document.all)
    window.copos[i] = document.all["c"+i]
else
    window.copos[i] = document.getElementById("c"+i);
nevar();
}

function nevar()
{
var x, y;
for (i = 0; i < copos.length; i++)
    {
    y = parseInt(window.copos[i].style.top);
    x = parseInt(window.copos[i].style.left);
    if (Math.random() > 0.5)
        y += parseInt(Math.random()+1);
    y += parseInt(Math.random()+2);
    window.copos[i].style.top = y;
    if (y > document.body.scrollTop + coposAlto)
        {
        window.copos[i].style.top = document.body.scrollTop-
        Math.round(Math.random()*10);
        window.copos[i].style.left =                 parseInt(Math.random()*coposAncho-1);
        }
    }
setTimeout("nevar()", coposVeloc);
}
< /script>