... but with three across,
A SimpleViewer gallery will, by default, have 3 columns of thumbnails positioned to the left of the main image.
You should not need to specifically set any options to achieve this layout. However, if your gallery currently sets thumbColumns="2", you will need to either set thumbColumns="3" or remove the entry entirely (to just use the default value of 3).
If you are looking to create many SimpleViewer gallery pages, then you might be interested in another one of our products: Showkase.
Showkase is a PHP web application which allows you to create complete portfolio web sites (integrating multiple galleries) online.
Showkase has full support for SimpleViewer-Pro (and Juicebox-Pro) galleries and the galleries can be created within the application itself in a web browser interface.
You can create Gallery Index pages and have as many galleries listed on each Gallery Index page as you wish.
Each gallery is represented by a thumbnail image with the gallery title displayed below and the gallery is opened when the user clicks on the image.
Demo sites can be found here and a sample Gallery Index page can be found here.
Another Gallery Index page (using a different theme) can be found here.
Showkase can also create non-gallery pages (About, Basic and Contact pages) where you can add information about yourself (or any other content you like).
All of this is done automatically within the Showkase interface without the need for any manual coding at all.
Showkase can be purchased as Showkase-Standard (which comes with SimpleViewer-Standard and Juicebox-Lite, the free versions) or Showkase-Pro (which comes with SimpleViewer-Pro and Juicebox-Pro).
The only difference between Showkase-Standard and Showkase-Pro is the bundled viewers.
As you already have SimpleViewer-Pro, you could purchase Showkase-Standard and upgrade it to use your SimpleViewer-Pro files by following the Installing a Pro Viewer instructions.
If you just mean more pages of thumbnails in a single gallery, then you can add as many thumbnails to your gallery as you like and SimpleViewer-Pro will automatically split the thumbnails into as many pages (of thumbColumns x thumbRows) as necessary.
SimpleViewer Support Team