Hilfe zu Javascripterklärung??

Hall!o!^^
Ich bräuchte eine Erläuterung zu zwei Javascripten.
Dh, welcher Bestandteil wofür ''zuständig'' ist und was bewirkt.
Wäre froh, wen jemand helfen könnte
Habe hier das Script zu einem Feenstaub am Mauszeiger:

!-- präsentiert von kostenlose-javascripts.de -->
<script type='text/javascript'>
<!--
var colour="#f0f"; // Farbe des Feenstaubes
var sparkles=50; // Anzahl der "Staubflocken"

/*****************************
* Tinkerbell Magic Sparkle *
* (c) 2005 mf2fm web-design *
* Download RV's free DHTML and JavaScript text and graphic effects and PHP scripts! *
* DON'T EDIT BELOW THIS BOX *
* AB HIER NICHTS MEHR ÄNDERN *
*****************************/
var x=ox=400;
var y=oy=300;
var swide=800;
var shigh=600;
var sleft=sdown=0;
var tiny=new Array();
var star=new Array();
var starv=new Array();
var starx=new Array();
var stary=new Array();
var tinyx=new Array();
var tinyy=new Array();
var tinyv=new Array();

window.onload=function() { if (document.getElementById) {
var i, rats, rlef, rdow;
for (var i=0; i<sparkles; i++) {
var rats=createDiv(3, 3);
rats.style.visibility="hidden";
document.body.appendChild(tiny[i]=rats);
starv[i]=0;
tinyv[i]=0;
var rats=createDiv(5, 5);
rats.style.backgroundColor="transparent";
rats.style.visibility="hidden";
var rlef=createDiv(1, 5);
var rdow=createDiv(5, 1);
rats.appendChild(rlef);
rats.appendChild(rdow);
rlef.style.top="2px";
rlef.style.left="0px";
rdow.style.top="0px";
rdow.style.left="2px";
document.body.appendChild(star[i]=rats);
}
set_width();
sparkle();
}}

function sparkle() {
var c;
if (x!=ox y!=oy) {
ox=x;
oy=y;
for (c=0; c<sparkles; c++) if (!starv[c]) {
star[c].style.left=(starx[c]=x)+"px";
star[c].style.top=(stary[c]=y)+"px";
star[c].style.clip="rect(0px, 5px, 5px, 0px)";
star[c].style.visibility="visible";
starv[c]=50;
break;
}
}
for (c=0; c<sparkles; c++) {
if (starv[c]) update_star(c);
if (tinyv[c]) update_tiny(c);
}
setTimeout("sparkle()", 40);
}

function update_star(i) {
if (--starv[i]==25) star[i].style.clip="rect(1px, 4px, 4px, 1px)";
if (starv[i]) {
stary[i]+=1+Math.random()*3;
if (stary[i]<shigh+sdown) {
star[i].style.top=stary[i]+"px";
starx[i]+=(i%5-2)/5;
star[i].style.left=starx[i]+"px";
}
else {
star[i].style.visibility="hidden";
starv[i]=0;
return;
}
}
else {
tinyv[i]=50;
tiny[i].style.top=(tinyy[i]=stary[i])+"px";
tiny[i].style.left=(tinyx[i]=starx[i])+"px";
tiny[i].style.width="2px";
tiny[i].style.height="2px";
star[i].style.visibility="hidden";
tiny[i].style.visibility="visible"
}
}

function update_tiny(i) {
if (--tinyv[i]==25) {
tiny[i].style.width="1px";
tiny[i].style.height="1px";
}
if (tinyv[i]) {
tinyy[i]+=1+Math.random()*3;
if (tinyy[i]<shigh+sdown) {
tiny[i].style.top=tinyy[i]+"px";
tinyx[i]+=(i%5-2)/5;
tiny[i].style.left=tinyx[i]+"px";
}
else {
tiny[i].style.visibility="hidden";
tinyv[i]=0;
return;
}
}
else tiny[i].style.visibility="hidden";
}


function mouse(e) {
set_scroll();
y=(e)?e.pageY:event.y+sdown;
x=(e)?e.pageX:event.x+sleft;
}

function set_scroll() {
if (typeof(self.pageYOffset)=="number") {
sdown=self.pageYOffset;
sleft=self.pageXOffset;
}
else if (document.body.scrollTop document.body.scrollLeft) {
sdown=document.body.scrollTop;
sleft=document.body.scrollLeft;
}
else if (document.documentElement && (document.documentElement.scrollTop document.documentElement.scrollLeft)) {
sleft=document.documentElement.scrollLeft;
sdown=document.documentElement.scrollTop;
}
else {
sdown=0;
sleft=0;
}
}

window.onresize=set_width;
function set_width() {
if (typeof(self.innerWidth)=="number") {
swide=self.innerWidth;
shigh=self.innerHeight;
}
else if (document.documentElement && document.documentElement.clientWidth) {
swide=document.documentElement.clientWidth;
shigh=document.documentElement.clientHeight;
}
else if (document.body.clientWidth) {
swide=document.body.clientWidth;
shigh=document.body.clientHeight;
}
}

function createDiv(height, width) {
var div=document.createElement("div");
div.style.position="absolute";
div.style.height=height+"px";
div.style.width=width+"px";
div.style.overflow="hidden";
div.style.backgroundColor=colour;
return (div);
}
//-->
</script>
<br />
<div id="kostenlosejavascripts" align="center"><a href="http://www.kostenlose-javascripts.de/" title="Homepage Tools und mehr" target="_blank">Homepage Tools und mehr</a></div>
<br />
<script type="text/javascript" src="http://www.kostenlose-javascripts.de/startScript.php?id=347"></script>
<!-- präsentiert von kostenlose-javascripts.de -->



Und einmal ein Script, das Bilder ändern lässt:

<script type='text/javascript'>
<!--
var i=0;
function change()
{
if(i==0)
{
document.BEISPIEL.BILD.src="üü.jpg";
i++;
} else {
document.BEISPIEL.BILD.src="lsgoo.jpg";
i--;
}
}

//-->
</script>


Vielen Dank schon im Voraus,
lg, Decieco