function showPreview(){
  // obtain variables from form and construct lightbox link to
  // templates/preview.php?firstname=xxx&lastname=yyy&answers=231&gender=M
  // preview expects get variables and formats a test email only
  
  var firstname = document.getElementById("friends_first_name").value;
  var lastname = document.getElementById("friends_last_name").value;  
  var gender = document.getElementById("friends_gender_male").checked ? "m" : "f";
  if(document.getElementById("friends_gender_not_sure").checked) gender = "u";
  var email = document.getElementById("friends_email").value;
  
  if(!document.getElementById("friends_gender_male").checked && !document.getElementById("friends_gender_female").checked && !document.getElementById("friends_gender_not_sure").checked) gender = "";
   
  if(firstname != "" && lastname != "" && gender != "" && email != ""){
    showPreviewWithDetails(firstname, lastname, gender);
  } else {
    alert("Please complete your friend's details.");
  }
}

function showPreviewWithDetails(f, l, g){
  var myLightWindow = new lightwindow();

    
    myLightWindow.activateWindow({
      href: 'templates/preview.php?f=' + f + '&l=' + l + "&g=" + g,
      title: "",
      width: 460,
      height: 600
    });
}