As you've noticed, Holiday Lights is two programs in one: It's a desktop decoration program that draws bulbs on your desktop while you work, and it's also a screen saver program. You can use both parts, or just one or the other.

 
Bulbs On the Desktop

The bulbs on the desktop are drawn by the Holiday Lights program. This program is started when you choose Programs -> Holiday Lights from the Start menu. It can also be started automatically when you turn on your computer, if you chose that option when you installed it.

If you don't want bulbs to be drawn on the desktop all the time, turn off the option to automatically start the program. To do this:

1. Open the Holiday Lights Settings window
2. Click the General tab
3. Uncheck the box marked Automatically Start Holiday Lights

Of course, if Holiday Lights isn't starting automatically but you'd like it to do so, you can check the box.

 
Holiday Lights As a Screen Saver

Whether you run the Holiday Lights program all the time or not, you can still use it as a screen saver.

Choose Holiday Lights from the list of screen savers in your Windows Display control panel, just as you would with any other screen saver.