Rain effect javascript code?

I'm trying to make it rain  on http://www.warriorcatsworld.net/forum , but I can't get whatever code I have been trying to use to work. Last night I managed to make it snow by using a code that was posted here as a Christmas/New Year's decoration, but rain won't work.

Do you have an image for the rain? If so could you post it.

I don't have a picture for the rain. Is that needed for the code?

Here's a pretty simple code

You can change how frequent the raindrops are, how fast they fall, and how many of them are on the screen at the time

Since you don't have a preferred image, I just used Google to find one.

Code:

<script type="text/javascript">
    var speed=20;
    var flakes=20;
    var flake_image="http://i57.tinypic.com/j99a3n.png";
    var swide, shigh;
    var dx=new Array();
    var xp=new Array();
    var yp=new Array();
    var am=new Array();
    var sty=new Array();
    window.onload=function() { if (document.getElementById) {
    var k, f, b;
    b=document.createElement("div");
    b.style.position="absolute";
    b.setAttribute("id", "bod");
    document.body.appendChild(b);
    set_scroll();
    set_width();
    for (var i=0; i<flakes; i++) {
    dx[i]=0;
    am[i]=Math.random()*20;
    xp[i]=am[i]+Math.random()*(swide-2*am[i]-25);
    yp[i]=Math.random()*shigh;
    sty[i]=0.75+1.25*Math.random();
    f=document.createElement("div");
    f.style.position="absolute";
    f.setAttribute("id", "flk"+i);
    f.style.zIndex=i;
    f.style.top=yp[i]+"px";
    f.style.left=xp[i]+"px";
    k=document.createElement("img");
    k.src=flake_image;
    f.appendChild(k);
    b.appendChild(f);
    }
    setInterval("winter_snow()", speed);
    }}
    window.onresize=set_width;
    function set_width() {
    if (document.documentElement && document.documentElement.clientWidth) {
    swide=document.documentElement.clientWidth;
    shigh=document.documentElement.clientHeight;
    }
    else if (typeof(self.innerHeight)=="number") {
    swide=self.innerWidth;
    shigh=self.innerHeight;
    }
    else if (document.body.clientWidth) {
    swide=document.body.clientWidth;
    shigh=document.body.clientHeight;
    }
    else {
    swide=800;
    shigh=600
    }
    }
    window.onscroll=set_scroll;
    function set_scroll() {
    var sleft, sdown;
    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;
    }
    document.getElementById("bod").style.top=sdown+"px";
    document.getElementById("bod").style.left=sleft+"px";
    }
    function winter_snow() {
    for (var i=0; i<flakes; i++) {
    yp[i]+=sty[i];
    if (yp[i]>shigh-30) {
    xp[i]=am[i]+Math.random()*(swide-2*am[i]-25);
    yp[i]=0;
    sty[i]=0.75+1.25*Math.random();
    }
    dx[i]+=0.02+Math.random()/10;
    document.getElementById("flk"+i).style.top=yp[i]+"px";
    document.getElementById("flk"+i).style.left=(xp[i]+am[i]*Math.sin(dx[i]))+"px";
    }
    }
    </script>

I got this from the Winter theme codes here on Forumotion, and don't own the code