Gram

$text = preg_replace("/\[youtube\]([\w\d\/\?=&:.\-]+)\[\/youtube\]/is","<object width=\"425\" height=\"344\"><param name=\"movie\" value=\"http://www.youtube.com/v/$1&hl=ru&fs=1\"></param><param name=\"allowFullScreen\" value=\"true\"></param><param name=\"allowscriptaccess\" value=\"always\"></param><embed src=\"http://www.youtube.com/v/$1&hl=ru&fs=1\" type=\"application/x-shockwave-flash\" allowscriptaccess=\"always\" allowfullscreen=\"true\" width=\"425\" height=\"344\"></embed></object>",$text);