Pruebas.



<script language="JavaScript">

colours=new Array('#ff0000','#00ff00','#ffffff','#ff00ff','#ffa500','#ffff00','#00ff00','#ffffff','ff00ff')
n = 10;
y = 0;
x = 0;
n6=(document.getElementById&&!document.all);
ns=(document.layers);
ie=(document.all);
d=(ns||ie)?'document.':'document.getElementById("';
a=(ns||n6)?'':'all.';
n6r=(n6)?'")':'';
s=(ns)?'':'.style';
if (ns){
for (i = 0; i < n; i++)
document.write('<layer name="dots'+i+'" top=0 left=0 width='+i/2+' height='+i/2+' bgcolor=#ff0000></layer>');
}
if (ie)
document.write('<div id="con" style="position:absolute;top:0px;left:0px">
<div style="position:relative">
');
if (ie||n6){
for (i = 0; i < n; i++)
document.write('<div id="dots'+i+'" style="position:absolute;top:0px;left:0px;width:'+i/2+'px;height:'+i/2+'px;background:#ff0000;font-size:'+i/2+'">
</div>
');
}
if (ie)
document.write('</div>
</div>
');
(ns||n6)?window.captureEvents(Event.MOUSEMOVE):0;
function Mouse(evnt){
y = (ns||n6)?evnt.pageY+4 - window.pageYOffset:event.y+4;
x = (ns||n6)?evnt.pageX+1:event.x+1;
}
(ns)?window.onMouseMove=Mouse:document.onmousemove=Mouse;
function animate(){
o=(ns||n6)?window.pageYOffset:0;
if (ie)con.style.top=document.body.scrollTop;
for (i = 0; i < n; i++){
var temp1 = eval(d+a+"dots"+i+n6r+s);

randcolours = colours[Math.floor(Math.random()*colours.length)];
(ns)?temp1.bgColor = randcolours:temp1.background = randcolours; 
if (i < n-1){
var temp2 = eval(d+a+"dots"+(i+1)+n6r+s);
temp1.top = parseInt(temp2.top);
temp1.left = parseInt(temp2.left);
} 
else{
temp1.top = y+o;
temp1.left = x;
}
}
setTimeout("animate()",10);
}
animate();
// -->
</script>

De nuevo en </body>, allá va el código:

 <script type="text/javascript">

var trailimage=["test.gif", 100, 99] //pon tu gif, el ancho (width) y el largo (height)
var offsetfrommouse=[10,-20] //Coloca la posición en píxeles.(X,Y) +X es derecha, -X izquierda; +Y es arriba, -Y es abajo. 0,0 para que no se mueva.
var displayduration=0 //duration in seconds image should remain visible. 0 for always.

if (document.getElementById || document.all)
document.write('<div id="trailimageid" style="position:absolute;visibility:visible;left:0px;top:0px;width:1px;height:1px">
<img src="'+trailimage[0]+'" border="0" width="'+trailimage[1]+'px" height="'+trailimage[2]+'px"></div>
')

function gettrailobj(){
if (document.getElementById)
return document.getElementById("trailimageid").style
else if (document.all)
return document.all.trailimagid.style
}

function truebody(){
return (!window.opera && document.compatMode && document.compatMode!="BackCompat")? document.documentElement : document.body
}

function hidetrail(){
gettrailobj().visibility="hidden"
document.onmousemove=""

}

function followmouse(e){
var xcoord=offsetfrommouse[0]
var ycoord=offsetfrommouse[1]
if (typeof e != "undefined"){
xcoord+=e.pageX
ycoord+=e.pageY
}
else if (typeof window.event !="undefined"){
xcoord+=truebody().scrollLeft+event.clientX
ycoord+=truebody().scrollTop+event.clientY
}
var docwidth=document.all? truebody().scrollLeft+truebody().clientWidth : pageXOffset+window.innerWidth-15
var docheight=document.all? Math.max(truebody().scrollHeight, truebody().clientHeight) : Math.max(document.body.offsetHeight, window.innerHeight)
if (xcoord+trailimage[1]+3>docwidth || ycoord+trailimage[2]> docheight)
gettrailobj().display="none"
else 
gettrailobj().display=""
gettrailobj().left=xcoord+"px"
gettrailobj().top=ycoord+"px"
}

document.onmousemove=followmouse

if (displayduration>0)
setTimeout("hidetrail()", displayduration*1000)

</script></code><br />

Agh, este gif me salió mal >w< en fin, ahi pueden ver el efecto <3

En </head>, allá va el código:



<script language="JavaScript">
<script type="text/javascript">
// <![CDATA[
var colour="#000000";
var sparkles=120;

/****************************
*  Tinkerbell Magic Sparkle *
* (c) 2005 mf2fm web-design *
*  http://www.mf2fm.com/rv  *
* DON'T EDIT BELOW THIS BOX *
****************************/
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";
}

document.onmousemove=mouse;
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 />