<form action="" method="post">
 <p>Ваш текст: <input type="text" name="hello" /></p>
</form>

<?php
if ($_POST){
$text = $_POST['hello'];
for ($i = 0; $i < mb_strlen($text,'UTF-8'); $i++)
{
$symbol = mb_substr($text,$i,1);
$varleft = $i*100;
$szfont = mt_rand(15,50);
echo "<div style='font-size:{$szfont};position:
absolute;left:{$varleft}px;top:50px;'> {$symbol} </div>";

}
}

?>