Ok looks like I got it all I have to do was to add a <p align="center"> & </p>
to the code & that center it right up.
if ($gallery->app->gallery_slideshow_type != "off" && $numPhotos != 0) {
$iconText = getIconText('display.gif', _("slideshow"));
$iconElements[] = '<p align="center"><a href="'. makeGalleryUrl("slideshow.php",array("set_albumName" => null)) .'">'. $iconText .'</a></p>';
To get the one for galleryDocs to work I had to added some extras ''' in a couple of different places.
if ($gallery->user->isAdmin()) {
$docsUrl = galleryDocs('admin');
if ($docsUrl) {
$iconText = getIconText('info.gif', _("documentation"));
$iconElements[] = '<p align="center"><a href=\"$docsUrl\'">'. $iconText .'</a></p>';