First, put a picture named dot.gif in an images folder in your website.

1) Insert this script anywhere inside the <BODY> section of your page.

<script language="JavaScript1.2">
// Snow Effect Script, Copyright 1999 Altan d.o.o. (snow@altan.hr, http://www.altan.hr/snow/index.html)*/
// Courtesy of SimplytheBest.net - http://simplythebest.net/scripts/
var no = 10;

var ns4up = (document.layers) ? 1 : 0; // browser sniffer
var ie4up = (document.all) ? 1 : 0;

var dx, xp, yp; // coordinate and position variables
var am, stx, sty; // amplitude and step variables
var i, doc_width = 800, doc_height = 600;

if (ns4up) {
doc_width = self.innerWidth;
doc_height = self.innerHeight;
} else if (ie4up) {
doc_width = document.body.clientWidth;
doc_height = document.body.clientHeight;
}

dx = new Array();
xp = new Array();
yp = new Array();
am = new Array();
stx = new Array();
sty = new Array();

for (i = 0; i < no; ++ i) {
dx[i] = 0; // set coordinate variables
xp[i] = Math.random()*(doc_width-50); // set position variables
yp[i] = Math.random()*doc_height;
am[i] = Math.random()*20; // set amplitude variables
stx[i] = 0.02 + Math.random()/10; // set step variables
sty[i] = 0.7 + Math.random(); // set step variables
if (ns4up) { // set layers
if (i == 0) {
document.write("<layer name=\"dot"+ i +"\" left=\"15\" top=\"15\" visibility=\"show\"><a href=\"http://inet.hr/\"><img src=\"images/dot.gif\" border=\"0\"></a></layer>");
} else {
document.write("<layer name=\"dot"+ i +"\" left=\"15\" top=\"15\" visibility=\"show\"><img src=\"images/dot.gif\" border=\"0\"></layer>");
}
} else if (ie4up) {
if (i == 0) {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: absolute; Z-INDEX: "+ i +"; VISIBILITY: visible; TOP: 15px; LEFT: 15px;\"><a href=\"http://inet.hr/\"><img src=\"images/dot.gif\" border=\"0\"></a></div>");
} else {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: absolute; Z-INDEX: "+ i +"; VISIBILITY: visible; TOP: 15px; LEFT: 15px;\"><img src=\"images/dot.gif\" border=\"0\"></div>");
}
}
}

function snowNS() { // Netscape main animation function
for (i = 0; i < no; ++ i) { // iterate for every dot
yp[i] += sty[i];
if (yp[i] > doc_height-50) {
xp[i] = Math.random()*(doc_width-am[i]-30);
yp[i] = 0;
stx[i] = 0.02 + Math.random()/10;
sty[i] = 0.7 + Math.random();
doc_width = self.innerWidth;
doc_height = self.innerHeight;
}
dx[i] += stx[i];
document.layers["dot"+i].top = yp[i];
document.layers["dot"+i].left = xp[i] + am[i]*Math.sin(dx[i]);
}
setTimeout("snowNS()", 10);
}

function snowIE() { // IE main animation function
for (i = 0; i < no; ++ i) { // iterate for every dot
yp[i] += sty[i];
if (yp[i] > doc_height-50) {
xp[i] = Math.random()*(doc_width-am[i]-30);
yp[i] = 0;
stx[i] = 0.02 + Math.random()/10;
sty[i] = 0.7 + Math.random();
doc_width = document.body.clientWidth;
doc_height = document.body.clientHeight;
}
dx[i] += stx[i];
document.all["dot"+i].style.pixelTop = yp[i];
document.all["dot"+i].style.pixelLeft = xp[i] + am[i]*Math.sin(dx[i]);
}
setTimeout("snowIE()", 10);
}

if (ns4up) {
snowNS();

} else if (ie4up) {
snowIE();
}
</script>


2) Define the number of images to render in this section of the script:

var no = 10;

3) Define the image name and its location in this section of the script:

document.write("<layer name=\"dot"+ i +"\" left=\"15\" top=\"15\" visibility=\"show\"><a href=\"http://inet.hr/\"><img src=\"images/dot.gif\" border=\"0\"></a></layer>");
} else {
document.write("<layer name=\"dot"+ i +"\" left=\"15\" top=\"15\" visibility=\"show\"><img src=\"images/dot.gif\" 

document.write("<div id=\"dot"+ i +"\" style=\"POSITION: absolute; Z-INDEX: "+ i +"; VISIBILITY: visible; TOP: 15px; LEFT: 15px;\"><a href=\"http://inet.hr/\"><img src=\"images/dot.gif\" border=\"0\"></a></div>");
} else {
document.write("<div id=\"dot"+ i +"\" style=\"POSITION: absolute; Z-INDEX: "+ i +"; VISIBILITY: visible; TOP: 15px; LEFT: 15px;\"><img src=\"images/dot.gif\" border=\"0\"></div>");

And here:

document.layers["dot"+i].top = yp[i];
document.layers["dot"+i].left = xp[i] + am[i]*Math.sin(dx[i]);

It may be easier to leave the image name to dot.gif and upload your own GIF using the name dot.gif and placing that in a subdirectory of where the script is called /images.