Submitting forms using “the_content” impossible?

Class Form
	{
		function show_form()
		{

			echo("
			<form method='post' action='index.php?page_id=4&temp_load=2' cellspacing='2'>
				<table>
					<tr>
						<td colspan='2' align='center'>
							<h2>Describe your Theme</h2>
							Please be as specific as possible.
						</td>
					</tr>
					<tr>
						<td colspan='2'>
						Theme Name(Required)<br />
						<input type='text' name='tn' />
						</td>
					</tr>
					<tr>
						<td colspan='2'>
						<input type='submit' name='s' value='Submit' />
						</td>
					</tr>
				</table>
			</form>
			");
		}
		function success()
		{
			if($_POST['tn'] == "test")
			{
				return "True";
			}
			else
			{
				return "False";
			}
		}

	}
	function form_replace($content)
	{
		$TEMP = new Form;
		$content = str_replace('[THEME-UPLOAD-SITE]',$TEMP->show_form(),$content);
		return $content;
	}
	function submitted($content)
	{
		$TEMP = new Form;
		$content = str_replace('[THEME-UPLOAD-SITE-2]',$TEMP->success(),$content);
		return $content;
	}

	if(!isset($_POST['s']))
	{
		add_filter('the_content','form_replace');
	}
	else
	{
		add_filter('the_content','submitted');
	}

Above is how my code is layed out, how can I fix it so when I submit the form it actually replaces the text when submitted?