当右边的滚动条拉到最下面的时候，按钮解除灰化

<script language="javascript">
<!--
function checkScrollBar()
   {
    var scrollLeft = document.forms[0].elements["txtAgreement"].scrollHeight - document.forms[0].elements["txtAgreement"].scrollTop;
    if(scrollLeft < 500)
    {
     document.forms[0].elements["Welcome:New"].disabled=false;
     document.forms[0].elements["Welcome:DonotAgree"].disabled=false;
     document.forms[0].elements["Welcome:Upgrate"].disabled=false;
    
    }
   }
//-->
</script>