Viendo el código fuente de la página lo podrías haber sacado.
Código HTML:
<script type="text/javascript">
var SNOW_Picture = "http://www.peters1.dk/billeder/snowflakes/snow1.gif"
var SNOW_no = 15;
var SNOW_browser_IE_NS;
var SNOW_browser_MOZ;
var SNOW_browser_IE7;
var SNOW_Time;
var SNOW_dx, SNOW_xp, SNOW_yp;
var SNOW_am, SNOW_stx, SNOW_sty;
var i, SNOW_Browser_Width, SNOW_Browser_Height;
//SNOW_Browser_Height = 2000;
SNOW_dx = new Array();
SNOW_xp = new Array();
SNOW_yp = new Array();
SNOW_am = new Array();
SNOW_stx = new Array();
SNOW_sty = new Array();
function SNOW_Weather()
{
for (i = 0; i < SNOW_no; ++ i)
{
SNOW_yp[i] += SNOW_sty[i];
if (SNOW_yp[i] > SNOW_Browser_Height-50)
{
SNOW_xp[i] = Math.random()*(SNOW_Browser_Width-SNOW_am[i]-30);
SNOW_yp[i] = 0;
SNOW_stx[i] = 0.02 + Math.random()/10;
SNOW_sty[i] = 0.7 + Math.random();
}
SNOW_dx[i] += SNOW_stx[i];
document.getElementById("SNOW_flake"+i).style.top=SNOW_yp[i]+"px";
document.getElementById("SNOW_flake"+i).style.left=SNOW_xp[i] + SNOW_am[i]*Math.sin(SNOW_dx[i])+"px";
}
SNOW_Time = setTimeout("SNOW_Weather()", 10);
}
jQuery(document).ready( function() {
////////////////////////////////////////////////////////////////
// Javascript made by Rasmus - http://www.peters1.dk //
////////////////////////////////////////////////////////////////
SNOW_browser_IE_NS = (document.body.clientHeight) ? 1 : 0;
SNOW_browser_MOZ = (self.innerWidth) ? 1 : 0;
SNOW_browser_IE7 = (document.documentElement.clientHeight) ? 1 : 0;
if (SNOW_browser_IE_NS)
{
SNOW_Browser_Width = document.body.clientWidth;
SNOW_Browser_Height = document.body.clientHeight;
}
else if (SNOW_browser_MOZ)
{
SNOW_Browser_Width = self.innerWidth - 20;
SNOW_Browser_Height = self.innerHeight;
}
else if (SNOW_browser_IE7)
{
SNOW_Browser_Width = document.documentElement.clientWidth;
SNOW_Browser_Height = document.documentElement.clientHeight;
}
for (i = 0; i < SNOW_no; ++ i)
{
SNOW_dx[i] = 0;
SNOW_xp[i] = Math.random()*(SNOW_Browser_Width-50);
SNOW_yp[i] = Math.random()*SNOW_Browser_Height;
SNOW_am[i] = Math.random()*20;
SNOW_stx[i] = 0.02 + Math.random()/10;
SNOW_sty[i] = 0.7 + Math.random();
if (i == 0) jQuery('body').prepend("<\div id=\"SNOW_flake"+ i +"\" style=\"position: absolute; z-index:200; visibility: visible; top: 15px; left: 15px;\"><a href=\"http://www.spiders-design.co.uk\" target=\"_blank\"><\img src=\""+SNOW_Picture+"\" border=\"0\"></a><\/div>");
else jQuery('body').prepend("<\div id=\"SNOW_flake"+ i +"\" style=\"position: absolute; z-index: 200; visibility: visible; top: 15px; left: 15px;\"><\img src=\""+SNOW_Picture+"\" border=\"0\"><\/div>");
}
SNOW_Weather();
});
</script> Ese es el de la pagina, tienes que pegarlo entre las etiquetas head.