Generally speaking when you insert a new record you will be taken to the detail page for that record automatically. So if you get to the detail page then the record inserted. You can add a URL parameter to the redirect to the detail page and use this as a trigger to display a message to the user about the successful upload.
On the insert page for the redirect URL you can set it like this:
$WA_redirectURL = "you_page.php?insert=1";
Then on the detail page you would have your success message wrapped in code like this:
<?php if(isset($_GET['insert'] && $_GET['insert'] == '1';){ ?>
You have successfully inserted a record to the db
<?php } ?>
On the insert page you could add in some custom code that will set a variable when the trigger for the insert has occurred. If the page gets to the insert but the insert does not occur this variable will still be set. You can then use this variable as the trigger to show the message about the insert failing. The code you would need on the insert page to show that the record was not inserted will look a little different. If you post back with the insert page I can take a look and let you know what I think.