How to Change a Windows XP Logon Wallpaper

1) Navigate to:
HKEY USERS\.DEFAULT\Control Panel\Desktop
2) Double click the wallpaper value, and type in the full path of your image and the filename.
3) To tile the image set "TileWallPaper" to 1
4) To Stretch the wallpaper set "WallPaperStyle" to 2
5) Close the registry editor and the changes will take place when you Log off.

For information about how to back up, restore, and edit the registry, click the following article numbers to view the Microsoft Knowledge Base articles:
256986 - Description of the Microsoft Windows Registry
322756 - HOW TO: Back Up, Edit, and Restore the Registry in Windows XP.