Yes, the snippet call is valid.. well &pics_in_a_row is renamed to &pics_per_row, but it doesn’t matter in this case.
The slidebox is not working on your site, because you have mootools included on that site (used by ajaxsearch). Slidebox uses scriptaculous/prototype, and they will collide with mootools.
You can use either smoothgallery display mode or slimbox display mode. Those both use mootools. You might also want to use &disable_js_libs=`1` in your snippet call to not include mootools twice on the page if it’s already always there.
Also, do you know about the &...._shadow_bgcolor parameters? If you use dropshadow in the thumbnails for example, you can use &thumb_shadow_bgcolor=`F0F3F2` (eg define it to the same as your background color) to make it not have the white bg below the shadow...
"He can have a lollipop any time he wants to. That's what it means to be a programmer."