You can't dissable the navigations in a webbrowser. But there are some workarounds.
Try to use an iframe, it should ignore the webrowser's direct navigation requests?
or make ONE page with php, that changes on each step, but still is the same page (and thus you can't navigate from it)
The following code is not complete, but it should show you a way to do it.
<?php
$Step = $_SESSION["step"];
if($Step == 1 && isset($_POST["name"]))
{
$Step = 2;
// save name
}else if($Step == 2 && isset($_POST["description"]))
{
$Step = 3;
// save description
}
if($Step == 1)
{ ?>
<html>
<body>
<form method="POST" action="">
<input name="name" type="text">
<input type="submit" value="ok">
</form>
</body>
</html>
<?php }else if($Step == 2){ ?>
<html>
<body>
<form method="POST" action="">
<input name="description" type="text">
<input type="submit" value="ok">
</form>
</body>
</html>
<?php } ?>