I am a total newbie to javascripts and I really couldn't figure out how this works. Could some please help me change this script to scroll up and down. Thank you very much.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

<head>
<title></title>
<style type="text/css">
/*<![CDATA[*/

.left {
position:fixed;right:100px;bottom:100px;
}

.right {
position:fixed;right:50px;bottom:100px;
}

/*]]>*/
</style></head>

<body>
<div style="width:3000px;height:50px;" ></div>
<div id="staticbuttons" style="position:absolute;">
<a href="javascript:" onmouseover="myspeed=-thespeed" onmouseout="myspeed=0"><img class="left"
src="arrows_up.gif" border="1" width="40" height="40"></a><br>
<a href="javascript:" onmouseover="myspeed=thespeed" onmouseout="myspeed=0"><img class="right"
src="arrows_dn.gif" border="1" width="40" height="40"></a>
</div>

<script>

//Page Scroller (aka custom scrollbar)- By Dynamic Drive
//For full source code and more DHTML scripts, visit http://www.dynamicdrive.com
//This credit MUST stay intact for use

var thespeed=3 //Enter scroll speed in integer (Advised: 1-3)
var myspeed=0


function scrollwindow(){
window.scrollBy(myspeed,0)
}

function initializeIT(){
if (myspeed!=0){
scrollwindow()
}
}

setInterval("initializeIT()",20)

</script>

</body>

</html>