function validateForm(thisform)
{
with (thisform)
	{		
			   if(first_name.value=="Name")first_name.value="";
		  	   if (emptyvalidation(first_name,"Please Enter Name")==false) 
				{
				 first_name.focus();
				 return false;
				}
				if(email.value=="Email")email.value="";
				if (emptyvalidation(email,"Please Enter Email")==false) 
			    {
			      email.focus();
			      return false;
			    }
				if (thisform.email.value)
				{
				if(emailvalidate(thisform)==false)
				{
					alert("Invalid Email Address");
					email.select();
					email.focus();
					return false;
				}
				}
				if(Phone.value=="Phone")Phone.value="";
			    if (emptyvalidation(Phone,"Please Enter Phone")==false) 
			    {
			       Phone.focus();
			       return false;
			    }			
				if(Comment.value=="Comment")Comment.value="";
				if (emptyvalidation(Comment,"Please Enter Comments")==false)
			    {
				Comment.focus();
				return false;
			    }
				if (userdigit.value==userdigit.defaultValue)
				{
				userdigit.value="";	
				}
				if(emptyvalidation(userdigit,"Please Enter veritification code")==false)
				{
				userdigit.focus();
				return false;
				}
				var pasurlq='email_validate.php';
				checkemaildomain('check_cemail',document.frmprocedures.email.value,pasurlq);
				return false;
	}
	thisform.submit();
	return true;
}
function captcha_refresh()
{
document.getElementById("button_div").src='button.php?'+Math.random();
return false;
}
<!--Ajax for checking the captcha code ends here -->
var xmlHttp
function runAjax(field,argurl,argVal)
{
//document.getElementById("check_captcha").innerHTML=" Loading...";
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
{
alert ("Browser does not support HTTP Request")
return
} 
var url=argurl
url=url+"?userdigit="+argVal
url=url+"&sid="+Math.random()
if(field=='check_captcha')
xmlHttp.onreadystatechange=check_captcha;
xmlHttp.open("GET",url,true)
xmlHttp.send(null)
}
function check_captcha() 
{ 
	if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
	{ 
			
			if(xmlHttp.responseText=="yes")
			{
						document.frmprocedures.submit();
			}
			else
			{
				captcha_refresh();
				alert("Verification code mismatch");
				document.frmprocedures.userdigit.focus();
				document.frmprocedures.userdigit.select();
				return false;
			}
			
	} 
} 
function checkemaildomain(field,argVal,argurl)
{
xmlHttp1=GetXmlHttpObject()
if (xmlHttp1==null)
{
alert ("Browser does not support HTTP Request")
return
} 
var url=argurl 
url=url+"?email="+argVal 
url=url+"&sid="+Math.random()
if(field=='check_cemail')
xmlHttp1.onreadystatechange=check_email;
xmlHttp1.open("GET",url,true)
xmlHttp1.send(null)
}
function check_email() 
{ 
	if (xmlHttp1.readyState==4 || xmlHttp1.readyState=="complete")
	{      
			if(xmlHttp1.responseText==0) 
			{
			 alert("Invalid e-mail id. Please enter valid e-mail id");
			 document.frmprocedures.email.focus();
			 document.frmprocedures.email.select();
			 return false;
			}
			else
			{
			runAjax('check_captcha','process_mail.php',document.frmprocedures.userdigit.value);
		    }
		 
	} 
}
function GetXmlHttpObject()
{ 
	var objXMLHttp=null
if (window.XMLHttpRequest)
{
	objXMLHttp=new XMLHttpRequest()
}
else if (window.ActiveXObject)
{
	objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP")
}
	return objXMLHttp
}
<!--Ajax for checking the captcha code starts here -->
function emptyvalidation(entered, alertbox)
{
		
	with (entered)
	{
		
	
		while (value.charAt(0) == ' ')
			value = value.substring(1);
		while (value.charAt(value.length - 1) == ' ')
			value = value.substring(0, value.length - 1);
		if (value==null || value=="")
		{
			if (alertbox!="") alert(alertbox);
			return false;
		}
		else return true;
	}
}
  function emailvalidate(thisform) 
 {
	
   var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
   var address = thisform.email.value;
   if(reg.test(address) == false)
   {
      //alert('Invalid Email Address');
      return false;
   }
  }
function emailvalidation(entered,alertbox)
{
	with (entered)
	{
		lastpos=value.length-1;//Total Letters
		apos=value.indexOf("@"); //Total letters before @
		dotpos=value.lastIndexOf(".");//Total letters before .
		beforeStr=value.substring(0,apos);
		afterStr=value.substring(apos);
		dotafatpos=afterStr.indexOf(".");
		udslpos=beforeStr.lastIndexOf("_");
		dotfpos=beforeStr.indexOf(".");
		dotlpos=beforeStr.lastIndexOf(".");
		if (apos<1 || dotpos-apos<2 || lastpos-dotpos>3 || lastpos-dotpos<2 || dotfpos!=dotlpos || apos-1==udslpos || dotafatpos==1) 
		{if (alertbox) {alert(alertbox);} return false; }
		else {return true;}
	}
}