First, show you some cool desktop wallpapers:




Now, follow the step by step guide, it is very easy and will bring you splendid idea to show your photos!
Step1. Launch Program and Choose Wallpaper Template After
downloading and installing the program, you can click the iCollage icon to launch and choose template from Desktop Wallpaper template.
Step 2: Add Photos and Start Editing
Drag your own photos into the templates and add Effect to photos by choosing specific photos and clicking Effect to choose your favorite effect for the photos. You can drag more photos than shown on the template and add frame to the added photos.
Step3: Output the wallpaper and set it as your own Desktop Wallpaper!

Ok, you can see details about
make desktop wallpaper on Mac Snow Leopard here:
http://www.imediacreator.com/mac-snow-leopard/how-to-make-desktop-wallpaper-on-snow-leopard.html#175