var speed=3

function movedown(mdiv){
var crossobj=document.getElementById(mdiv)
var contentheight=crossobj.offsetHeight
if (parseInt(crossobj.style.top)>=(contentheight*(-1)+100))
crossobj.style.top=parseInt(crossobj.style.top)-speed+"px"
movedownvar=setTimeout("movedown('"+mdiv+"')",20)
}

function moveup(mdiv){
var crossobj=document.getElementById(mdiv)
var contentheight=crossobj.offsetHeight
if (parseInt(crossobj.style.top)<=0)
crossobj.style.top=parseInt(crossobj.style.top)+speed+"px"
moveupvar=setTimeout("moveup('"+mdiv+"')",20)

}