The short answer is you can't.
You're doing a $_GET, which is used to retrieve form values:
The built-in $_GET function is used to collect values in a form with method="get".
In other words, if on your page you had:
<form method="get" action="blah.php"> <input name="test"></input> </form>
Your $_GET call would retrieve the value in that input field.
Then, when the user clicks your submit button, he/she will be issuing a "GET" request to blah.php, sending along the value in 'test'.
If you did want to go down the second path, you'd be looking at XMLHttpRequest, or my preference, jQuerys Ajax calls: http://docs.jquery.com/Ajax