function checkinput()
   {
       if(document.getElementById('username').value=="")
        {
	        document.getElementById('checkresult').innerHTML="<font color='#009900'>用户名不能为空。</font>";
	        document.getElementById('username').focus();
	        return false;
        }
        else if(document.getElementById('password').value=="")
        {
	        alert('请输入密码！');
	        document.getElementById('password').focus();
	        return false;
        }
        else if(document.getElementById('password').value=="" != document.getElementById('password2').value=="")
        {
	        alert('两次密码输入必须相同！');
	        document.getElementById('password2').focus();
	        return false;
        }
        return true;
   }