I have exactly the same problem.

Lightbox does not work with default semantic template

(Other templates work)

I have the same problem as well. This whole forum seems to excist of requests for help only and very little answers...  The support doesn't reflect the great component.

couple of things with Lightbox to make it work easily...

A: are you running 1.5 or 1.0?

1.5 has built in MooTools which all that has to be added to the template is a simple line to enable the loading of the mootools which includes some built in lightbox functions to Joomla 1.5

The below Link Helped me with this greatly..
http://tutorials.yootheme.com/index.php?option=com_mtree&task=viewlink&link_id=78&Itemid=2

in 1.5 just add this:
JHTML::_('behavior.mootools');

so it looks like this:
// no direct access
defined('_JEXEC') or die('Restricted access');
JHTML::_('behavior.mootools');

Not exactly done yet... but it might work with this config.  I usually add the next items as well.

I usually use an additional effects engine... rokbox / yooeffects / avreloaded.. all free.. Yooeffects has been my latest testing and so far so good.  However rokbox also works quite well too.

Give it a shot and let me know.  still some browser issues I see with RSGallery...

My questions is how to remove the branding from RSGallery... I know the normal config you can turn it off but when I create a menu that links to the component the name in the title of the page is RSGallery2.  Would rather it be the title of the gallery or Menu Item.  Nothing major though...