Скрипт для снежинок. а правильней будет, скрипт падающих предметов.
<SCRIPT language=JavaScript>
<!--
Amount=30;

Image0=new Image();
Image0.src="http://fantasyflash.ru/script/web/image/sneg1.gif";

grphcs=new Array(1)
grphcs[0]="http://fantasyflash.ru/script/web/image/sneg1.gif"

Ypos=new Array();
Xpos=new Array();
Speed=new Array();
Step=new Array();
Cstep=new Array();
ns=(document.layers)?1:0;
if (ns){
for (i = 0; i < Amount; i++){
var P=Math.floor(Math.random()*grphcs.length);
rndPic=grphcs[P];
document.write("<LAYER NAME='sn"+i+"' LEFT=0 TOP=0><img src="+rndPic+"></LAYER>");
}
}
else{
document.write('<div style="position:absolute;top:0px;left:0px"><div style="position:relative">');
for (i = 0; i < Amount; i++){
var P=Math.floor(Math.random()*grphcs.length);
rndPic=grphcs[P];
document.write('<img id="si" src="'+rndPic+'" style="position:absolute;top:0px;left:0px">');
}
document.write('</div></div>');
}
WinHeight=(document.layers)?window.innerHeight:window.document.body.clientHeight;
WinWidth=(document.layers)?window.innerWidth:window.document.body.clientWidth;
for (i=0; i < Amount; i++){
Ypos[i] = Math.round(Math.random()*WinHeight);
Xpos[i] = Math.round(Math.random()*WinWidth);
Speed[i]= Math.random()*3+2;
Cstep[i]=0;//osw
Step[i]=Math.random()*0.1+0.05;
}
function fall(){
var WinHeight=(document.layers)?window.innerHeight:window.document.body.clientHeight;
var WinWidth=(document.layers)?window.innerWidth:window.document.body.clientWidth;
var hscrll=(document.layers)?window.pageYOffset:document.body.scrollTop;
var wscrll=(document.layers)?window.pageXOffset:document.body.scrollLeft;//fantasyflash.ru
for (i=0; i < Amount; i++){
sy = Speed[i]*Math.sin(90*Math.PI/180);
sx = Speed[i]*Math.cos(Cstep[i]);
Ypos[i]+=sy;
Xpos[i]+=sx;
if (Ypos[i] > WinHeight){
Ypos[i]=-60;
Xpos[i]=Math.round(Math.random()*WinWidth);
Speed[i]=Math.random()*5+2;
}
if (ns){
document.layers['sn'+i].left=Xpos[i];
document.layers['sn'+i].top=Ypos[i]+hscrll;
}
else{
si[i].style.pixelLeft=Xpos[i];//osw
si[i].style.pixelTop=Ypos[i]+hscrll;
}
Cstep[i]+=Step[i];
}
setTimeout('fall()',50);
}
fall()
//-->
</SCRIPT>