form select with ajax

form select with ajax

I'm building a bug tracker tool.
When you create a project, you can change the project status (open, in
progress & finished) on the project page using this select form:
<form action="classes/projectStatus.class.php" method="post">
<label> Change Project Status </label>
<select name="status" id="status">
<option value="Open">Open</option>
<option value="In Progress">In Progress</option>
<option value="Finished">Finished</option>
</select>
<input type='hidden' name='hdnID' value="<?php echo $id;?>">
<input class="small button" value="Change Status" type="submit">
</form>
This is the projectStatus.class.php file:
$status = $_POST['status'];
$id = $_POST['hdnID'];
$sql="UPDATE projects SET status = '$status'";
$result = mysql_query($sql);
$result = mysql_real_escape_string($sql);
if($result){
header('Location: ../projectpage.php?id='.$id);
} else {
echo "There is something wrong. Try again later."; }
mysql_close();
How can I do this with AJAX? Could anybody provide me with some right code?!
I know the form isn't sql injection proof and I don't use mysqli, I will
change this, but first I'd like to have an answer :).
Thanks!