Change The Default Logon Wallpaper and/or Screen Saver

1. Open the Registry Editor (Start > Run: regedit)
2. Navigate to the key HKEY_USERS\.DEFAULT\Control Panel\Desktop
3. Replace the data of the values Wallpaper and SCRNSAVE.EXE with the path of the new wallpaper and screensaver files

Notes:
The wallpaper file must be a .bmp image file (24-bit bitmap).