Вот рабочая функция
function AutoLinkUrls($str,$popup = FALSE){
if (preg_match_all("#(^|\s|\()((http(s?)://)|(www\.))(\w+[^\s\)\<]+)#i", $str, $matches)){
$pop = ($popup == TRUE) ? " target=\"_blank\" " : "";
for ($i = 0; $i < count($matches['0']); $i++){
$period = '';
if (preg_match("|\.$|", $matches['6'][$i])){
$period = '.';
$matches['6'][$i] = substr($matches['6'][$i], 0, -1);
}
$str = str_replace($matches['0'][$i],
$matches['1'][$i].'</xmp><a href="http'.
$matches['4'][$i].'://'.
$matches['5'][$i].
$matches['6'][$i].'"'.$pop.'>http'.
$matches['4'][$i].'://'.
$matches['5'][$i].
$matches['6'][$i].'</a><xmp>'.
$period, $str);
}//end for
}//end if
return $str; }