[S@NL - BlackBik]

This (in bold)

if (stristr($navigator_user_agent, "msie")) {    
    return '<a href="' .  $link . '" target="_blank"><img src="' .  $link . '" border="0" alt="" style="width: expression(this.width > 640 ? 480  : true);" /></a>';    
} else {    
    return '<a href="' .  $link . '" target="_blank"><img src="' .  $link . '" border="0" alt="" style="max-width: 730px;" /></a>';    
}

If you're using my version, it's the same lines

In the first line, the number after the greater then sign is the width above wich the hack will resize for Internet Explorer
In the second line the number is just the width above wich the hack will do it's worst for Firefox and other browsers