Zo dus

<style type="text/css">
.num {
float: left;
color: #FFFFFF;
font-size: 13px;
font-family: monospace;
text-align: right;
background-color:#999999;
margin-right: 6pt;
padding-right: 6pt;
border-right: 1px solid gray;}

body {margin: 0px; margin-left: 5px;
background-color:#F7F7F7;}
td {vertical-align: top;}
code {white-space: nowrap;}

</style>
<?php
function highlight_num($file)
{
$lines = implode(range(1, count(file($file))), '<br />');
$content = highlight_file($file, true);

echo "<table><tr><td class=\"num\">\n$lines\n</td><td>\n$content\n</td></tr></table>";
}

highlight_num('index.php');
?>