Getting a specific Vimeo thumbnail size via cURL/PHP building on http://www.soapboxdave.com/2010/04/getting-the-vimeo-thumbnail/

gistfile1.txt

function vimeo_thumb_size( $id, $size = 'large' ) {

    // Sanitize the variables
	$id = esc_attr( $id );
	$size = esc_attr( $size );

	// Stop if no video ID entered
	if ( empty( $id ) )
		return 'Error - no video ID specified';

    if (!function_exists('curl_init')) die('cURL is not installed!');
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "http://vimeo.com/api/v2/video/$id.php");
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_TIMEOUT, 10);
    $output = unserialize(curl_exec($ch));
    $output = $output[0];
    curl_close($ch);

    if ( 'small' == $size ) {
		return $output["thumbnail_small"];
	} elseif ( 'medium' == $size ) {
		return $output["thumbnail_medium"];
	} else {
		return $output["thumbnail_large"];
	}

}