Windows

• 1). Click "Start" and open the "Control Panel." Navigate to "Appearance and Personalization" and click "Adjust screen resolution." In the Windows XP Control Panel, double-click "Display" and go to the "Settings" tab. Look at the pixel values next to your screen resolution to get an idea of the right size wallpaper.
  
  
• 2). Click the "Desktop Background" tab, or the "Desktop" tab if you're using Windows XP. Click "Browse" to open a file browser on your computer. Find the image you want to set as your wallpaper, and double-click the file.
  
  
• 3). Click "Apply" and "OK" to make the changes. Alternatively, right-click any image on the Internet and choose "Set image as background." Right-click the image again and choose "Save image as" if you like the wallpaper and want to save a copy on your hard drive.
  
  

Mac OS X

• 1). Click "System Preferences" in your Dock. Click "Displays" and make a note of the highlighted dimensions under "Resolution." The size of your wallpaper should match this amount fairly closely.
  
  
• 2). Click "Show All." Click "Desktop and Screen Saver." Choose any of the desktop backgrounds in your "Apple" folder, or click the arrow next to "Folders" to open a hard drive folder that contains your personal images.
  
  
• 3). Click an image to change the background instantly. Check the box next to "Change picture every 30 minutes" to cycle through all pictures in the selected folder.
  
  
• 4). Hold down the "Command" key and press "Q" to quit System Preferences.