var SNOW_Picture = "snow.png";
var SNOW_no = 68;

var SNOW_browser_IE_NS = (document.body.clientHeight) ? 1 : 0;
var SNOW_browser_MOZ = (self.innerWidth) ? 1 : 0;

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;

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;
}

SNOW_dx = new Array();
SNOW_xp = new Array();
SNOW_yp = new Array();
SNOW_am = new Array();
SNOW_stx = new Array();
SNOW_sty = new Array();

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) document.write("<\div id=\"SNOW_flake"+ i +"\" style=\"position: absolute; z-index: "+ i +"; visibility: visible; top: 15px; left: 15px;\"><a href=\"http://www.peters1.dk\" target=\"_blank\"><\img src=\""+SNOW_Picture+"\" border=\"0\"></a><\/div>");
else document.write("<\div id=\"SNOW_flake"+ i +"\" style=\"position: absolute; z-index: "+ i +"; visibility: visible; top: 15px; left: 15px;\"><\img src=\""+SNOW_Picture+"\" border=\"0\"><\/div>");
}

function SNOW_Weather()
{

for (i = 0; i < SNOW_no; ++ i)
{
SNOW_yp[i] += SNOW_sty[i];

if (SNOW_yp[i] > SNOW_Browser_Height+2500)
{
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);

}

SNOW_Weather();

<script type="text/javascript" src="http://www.tvojsajt.com/snow.js"></script>