function validate_form()
{
    var errorString = "";
    var contact_form = document.contact_form;
    var name, email, phone, message;
                      
    add_tracking_fields(contact_form);

    if ( contact_form.name != undefined && contact_form.name.value == "" )
    {
        errorString = errorString + "Please enter a name. \n";
    }
    else
    {
        name = contact_form.name.value;
    }
    
    
    if ( contact_form.email != undefined )
    {
        if(contact_form.email.value == "")
        {
            errorString = errorString + "Please enter a valid email address. \n";
        }
        else if ( (contact_form.email.value.indexOf(".") < 1) || (contact_form.email.value.indexOf("@") < 1) )
        {
            errorString = errorString + "Please enter a valid email address. \n";
        }
        else
        {
            email = contact_form.email.value;
        }
    }
    
    
    if ( contact_form.phone != undefined && contact_form.phone.value == "" )
    {
        errorString = errorString + "Please enter a phone number. \n";
    }
    else
    {
        phone = contact_form.phone.value;
    }
    
    
    if ( contact_form.message != undefined && contact_form.message.value == "" )
    {
       // errorString = errorString + "Please enter a message. \n";
    }
    else
    {
        message = contact_form.message.value;
    }
    
    
    if (errorString != "")
    {
        alert(errorString);
        return false;
    }
    else
    {
        return true;
    }
}