function validate_required(field,alerttxt)
    {
    with (field)
      {
      if (value==null||value=="")
        {
        alert(alerttxt);return false;
        }
      else
        {
        return true;
        }
      }
    }
    function validate_email(field,alerttxt)
    {
    with (field)
      {
      apos=value.indexOf("@");
      dotpos=value.lastIndexOf(".");
      if (apos<1||dotpos-apos<2)
        {alert(alerttxt);return false;}
      else {return true;}
      }
    }
    
    function validate_form(thisform)
    {
    with (thisform)
      {
      if (validate_required(name,"Your name is missing, please complete this field")==false)
      {name.focus();return false;}
      if (validate_required(company,"Your company is missing, please complete this field")==false)
      {company.focus();return false;}
      if (validate_required(email,"Your e-mail address is missing, please complete this field")==false)
      {email.focus();return false;}
      if (validate_email(email,"Sorry, you have entered an incorrect e-mail address, please enter a correct email")==false)
      {email.focus();return false;}
      if (validate_required(telephone,"Your telephone number is missing, please complete this field")==false)
      {telephone.focus();return false;}
      if ( ( contactby[0].checked == false ) && ( contactby[1].checked == false ) ) { alert ( "Please choose how you would prefer to be contacted" ); return false; } 
  	  if (validate_required(enquirydetails,"The details of your enquiry is missing, please complete this field")==false)
      {enquirydetails.focus();return false;}
      }
    
    }