how to make auto scroll from down to up?

<SCRIPT language=JavaScript1.2>
//change 1 to another integer to alter the scroll speed. Greater is faster

var speed=1

var currentpos=0,alt=1,curpos1=0,curpos2=-1

function initialize(){

startit()

}

function scrollwindow(){

if (document.all &&

!document.getElementById)

temp=document.body.scrollTop

else

temp=window.pageYOffset

if (alt==0)

alt=2

else

alt=1

if (alt==0)

curpos1=temp

else

curpos2=temp

if (curpos1!=curpos2){

if (document.all)

currentpos=document.body.scrollTop+speed

else

currentpos=window.pageYOffset+speed

window.scroll(0,currentpos)

}

else{

currentpos=0

window.scroll(0,currentpos)

}

}

function startit(){

setInterval("scrollwindow()",50)

}

window.onload=initialize

</SCRIPT>