Resizing image's thumbnail

[grandgefx]

Hi, I need to resize the image’s thumbnail, how can I do it?
this my php code, which part of the code that I need to change or add?
I want to resize the thumbnail to 100x67
[php]?php
for($i=1;$i<10;$i++)
{
if(!empty($foto[$i]))
{
if($i==1)
{
$foto_first=$foto[$i];
}
echo “”;
$dataku.="’".$foto[$i]."’: { thumbnail: ‘thumb/".$foto[$i]."’},";
}
else
{
$i–;
break;
}
}

$dataku=substr($dataku,0,-1);
?>

<link rel="stylesheet" href="css/slideshow.css">

<script src="js/mootools-1.3.1-core.js"></script>
<script src="js/mootools-1.3.1.1-more.js"></script>
<script src="js/slideshow.js"></script>
<script src="js/slideshow.flash.js"></script>
<script>
	window.addEvent('domready', function(){
		var data = { <?php echo $dataku;?>};

new Slideshow.Flash(‘flash’, data, { color: [‘tomato’],duration: 1500, delay: 10000, height: 400, hu: ‘conf/i/’, width: 500});
});

<div style="padding-bottom:350px;padding-right:100px">
<div id="flash" class="slideshow">
	<img src="conf/i/<?php echo $foto_first; ?>" alt="1" height=100px><br>
</div>
</div>

[/php]