function IsEmpty(aTextField) {
   if ((aTextField.value.length==0) ||
   (aTextField.value==null)) {
      return true;
   }
   else { return false; }
} 

function IsNumeric(sText)

{
   var ValidChars = "0123456789.()- ";
   var IsNumber=true;
   var Char;

 
   for (i = 0; i < sText.length && IsNumber == true; i++) 
      { 
      Char = sText.charAt(i); 
      if (ValidChars.indexOf(Char) == -1) 
         {
         IsNumber = false;
         }
      }
   return IsNumber;
   
   }

function IsValidEmail(str) {

   return (str.indexOf(".") > 2) && (str.indexOf("@") > 0);
 


}



function validate(form)
{

if(IsEmpty(form.firstname)) 
   { 
      alert('Please enter your first name') 
      return false; 
   } 

if(IsEmpty(form.lastname)) 
   { 
      alert('Please enter your last name') 
      return false; 
   }

if(IsEmpty(form.email)) 
   { 
      alert('Please enter your email address') 
      return false; 
   } 

if(!IsValidEmail(form.email.value)) 
   { 
      alert('Please enter a valid email address') 
      return false; 
   } 
 
}