Downloading skins for Style XP requires downloading all the elements that make up a skin, such as theme elements, visual styles, and logon and boot screens. In Style XP all these elements can be applied under a new theme name, letting you easily apply all these elements at once by selecting that theme in Style XP.
Numerous skin elements are available for download, so even if you don't want to create your own backgrounds, icon sets, or visual styles, you can mix and match elements from existing skins (those you have downloaded) and then apply them to your computer. You are, in essence, creating a unique skin in this manner.
As you download skin elements from the various skin websites, the download of a background might include other skin elements. So, sometimes you get more elements than you were expecting. This is great in terms of increasing the elements you have saved in your skin library.