Browsers remember the last request they sent to the webserver, which is why a refresh makes your script submit data again.
You can get around this by making the browser remember something else;
After processing the post, redirect the user to the script using a clean request:
Header('Location: yourscript.php');
make sure that you do not print anything if the submit was ok, just do the header and exit the script.
A forum, a FAQ, email notification, what else do you need?
