The idea of the themes is to able to change some of the default look and feel of the clock. I have a couple that I've made, but I'm not that good with photo editors so, I think they need some work. I also don't know the best way to get them to you. So, for now, you can create them manually. When the application is installed, it should create a /DeskClockPlus/Themes folder on your SD card. Each theme will have it's own folder and the folder name will also serve as the name of the theme. The theme folder will have one or more of the following files:
The background image will be scaled to fit the size of your screen. It's also currently scaling from the middle so, based upon screen dimensions, image dimensions, some of the image may be cut off. However, the entire screen will display the image
The Dock is the bar at the bottom that will house the five icons. It's size (480 X 84) and position of the buttons are based off the dock themes for LauncherPro. You can find a ton of different docks in this thread.
The buttons are simply 56 X 56 square pictures. You can do pretty much what you like with them. However, the order of the buttons don't change (for now).