Help! Gallery thumbnails wrong size and wrong display.

I want my gallery thumbnails to be horizontal, rather than square or vertical. Also, I want them to align properly. On the page I’m referencing, the thumbnails are vertical, and they are not lined up properly. Please have a look:

http://desertspringspublishing.com/self-publishing/entertaining-your-way/

I need to get this fixed ASAP!

Please help.