Code
<Body OnLoad="scrollln()">
<Script Language="JavaScript">
var pos=1
var text=prompt('Ваш текст','Ваш текст')
function scrollln()
{document.running.text.value=text.substring(0,pos)
if(pos>=text.length)
{pos=1
window.setTimeout("scrollOut()",300)}
else
{ pos++
window.setTimeout("scrollln()",50)}}
function scrollOut()
{document.running.text.value=text.substring(pos,text.length)
if(pos>=text.length)
{pos=1
window.setTimeout("scrollln()",100) }
else
{pos++
window.setTimeout("scrollOut()",50)}}
</Script>
<Form Name="running"><Input Name="text" Size="15"></Form>