<?php
    function highlight($code)
    {
        $code    =    highlight_string($code,true);
        $code    =    str_replace('</code>1','</code>',$code);
        return $code;
    }
?>
(........)
<textarea rows="10" cols="75" name="phpcode"><?php echo highlight($code); ?></textarea>

<code><span style="color: #000000">
<span style="color: #0000BB"><?php
<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'test'</span><span style="color: #007700">;
<br /></span><span style="color: #0000BB">?></span>
</span>
</code>