To customize the appearance of the icons on a Vista desktop, right click any blank area of the desktop and point to View. Select Large, Medium or Classic for the icon size. Select Auto Arrange to let Vista decide where the icons should be placed. Select Align to Grid in order to snap the icons to the desktop's invisible grid. If they are not aligned to the grid, you can move them around and place them precisely where you want them.
Much like the View options, the Sort By, Refresh and New options provided when you right click the desktop work much the same as they do in XP. Sort By allows you to change the manner in which icons are sorted, and Refresh will update the desktop following any changes. New displays a menu, making it easy to create everything from a new text document to a new briefcase.
At the bottom of the right click menu is an option labeled Personalize. Clicking this will bring up the Personalization window, which is where most of your Vista desktop customization will begin.
To change an icon, click Change Desktop Icons in the task pane of the Personalization window. In the Desktop Icon Settings dialog, select the program whose icon you want to change and click Change Icon. Click Browse, find the icon you want to use and click OK and then Apply.