Sending POST (or GET) data to a PHP script using AJAX

I'm trying to build a simple "I viewed this" function in a php directory for an intranet site.

So when a user has read the page, they click a button at the bottom that says "I've read this" that sends the users User ID and the page ID to a simple database table that I can then harvest for other uses.

I'm trying to do it with AJAX and PHP.

Here's my code:

<SCRIPT LANGUAGE="JavaScript">
function viewSave(form) {
var itemid = <?php echo $itemid; ?>;
var userid = <?php echo $userid; ?>;

var xmlhttp;

if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }

 xmlhttp.open("GET","saveView.php?q=itemid="+itemid+"&userid="+userid,true);
 xmlhttp.send();
}

</script>   

and I've set up a simple form with hidden fields:

<form onSubmit="return viewSave(this)" >
<input type="submit" name="submit" value="Save" />
</form>

When I click submit, the URL changes and I get my variables, like this:

thispage.php?itemid=455&userid=999&submit=Save

but "saveView.php" is not called and the data is not sent.

Here's what's in saveView.php:

<?php


$userid =$_GET["userid"];
$itemid = $_GET["itemid"];

  // Connect to the database
            $dbc = mysqli_connect('localhost', 'root', '', 'viewsave');

            // Write the data to the database
            $query = "INSERT INTO saves (entryID, userid, itemid) VALUES ( '0', '$userid', '$itemid')";
            mysqli_query($dbc, $query);

?>

I'm guessing the URL params are only appearing because of the form and that there's something wrong with the JavaScript.

I'm only a beginner with JS.

Help appreciated.

Ray.