Windows 7 comes with some very nice new wallpapers, also we can customize to slide show our desktop with wallpapers we like.
1.Right-click an empty part of the desktop, select Personalize.
2.Click Desktop background(slide show).

3.Now in the New windows select wallpapers you like as your desktop.You can select from windows themes or from other location of your computer.You can hold down Ctl to select multiple wallpapers.Also you can customize your wallpaper location and so on.

4.Done,click Save Changes to enable your customizing.