<script language="javascript">
function ok()
{with (document.form)
{
c.value=a.value*b.value
}
}
</script>
<form name="form">
<input name="a" type="text" size="6"/>×<input name="b" type="text" size="6" onkeyup='javascript:ok();'/>
=<input name="c" type="text" value="" size="6"/>
</form>