[kh99]

Oh I see. OK, then I think you just want this:

$smallwords = array( 'of','a','the','and','an','or',
'nor','but','is','if','then','else','when', 'at','from',
'by','on','for','in','to','into','with' );

$words = explode(' ', $thread['title']);

foreach ($words as $key => $word) {
    if (!$key or !in_array($word, $smallwords)) $words[$key] = ucwords(strtolower($word));
}

and I don't know what follows, I guess an implode?