function url_hilight($str)
{   
    // lift all links, images and image maps
    $url_tags = array (
                     "'<a[^>]*>.*</a>'si",
                     "'<map[^>]*>.*</map>'si",
                     "'<script[^>]*>.*</script>'si",
                     "'<style[^>]*>.*</style>'si",
                     "'<applet[^>]*>'si",
                     "'<object[^>]*>'si",
                     "'<embed[^>]*>'si",
                     "'<link[^>]*>'si",
                     "'<img[^>]*>'si"
                      );
    foreach($url_tags as $url_tag)
    {
        preg_match_all($url_tag, $str, $matches, PREG_SET_ORDER);
        foreach($matches as $match)
        {
            $key = "<" . md5($match[0]) . ">";
            $search[] = $key;
            $replace[] = $match[0];
        }
    }

    $str = str_replace($replace, $search, $str);

    // indicate where urls end if they have these trailing special chars
    $sentinals = array("'&(quot|#34);'i",                 // Replace html entities
                       "'&(lt|#60);'i",
                       "'&(gt|#62);'i",
                       "'&(nbsp|#160);'i",
                       "'&(iexcl|#161);'i",
                       "'&(cent|#162);'i",
                       "'&(pound|#163);'i",
                       "'&(copy|#169);'i",
                       "'&#(d+);'e");
    $str = preg_replace($sentinals, "<sentinal>\0<sentinal>", $str);

    $vdom = "[:alnum:]";                // Valid domain chars
    $vurl = $vdom."_~-";                // Valid subdomain and path chars
    //$vura = "À-ßà-ÿ!#$%&*+,;=@.".$vurl; // Valid additional parameters (after '?') chars;
    $vura = "À-ßà-ÿ!#$%&*+,;=@./".$vurl; // Valid additional parameters (after '?') chars;
                                        // insert other local characters if needed
    $protocol = "[[:alpha:]]{3,10}://"; // Protocol exp
    $server = "([$vurl]+[.])*[$vdom]+"; // Server name exp
    $path = "(([$vurl]+([.][$vurl]+)*/)|([.]{1,2}/))*"; // Document path exp (/.../)
    $name = "[$vurl]+([.][$vurl]+)*";   // Document name exp
    $params = "[?][$vura]*";            // Additional parameters (for GET)

    $str = eregi_replace("$protocol$server(/$path($name)?)?($params)?",  "<a href="\0">\0</a>", $str); // URL into links


    $str = str_replace("<sentinal>", '', $str);
    return str_replace($search, $replace, $str);
}