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,"sorry, but the name field is required")==false)
{name.focus();return false}
if (validate_required(company,"sorry, but the company field is required")==false)
{company.focus();return false}
if (validate_required(email,"sorry, but the email field is required")==false)
{email.focus();return false}
if (validate_required(phone,"sorry, but the phone field is required")==false)
{phone.focus();return false}

if (validate_required(Category,"sorry, but the vehicle type field is required")==false)
{comment.focus();return false}
if (validate_required(SubCat,"sorry, but the chassis type field is required")==false)
{comment.focus();return false}
if (validate_required(SubCat2,"sorry, but the vehicle length field is required")==false)
{comment.focus();return false}
if (validate_required(SubCat3,"sorry, but the no. doors field is required")==false)
{comment.focus();return false}
if (validate_required(SubCat4,"sorry, but the no. seats field is required")==false)
{comment.focus();return false}
if (validate_required(SubCat5,"sorry, but the star rating field is required")==false)
{comment.focus();return false}

if (validate_email(email,"sorry, but I think you've made a mistake with your email address...")==false)
  {email.focus();return false}

}
}