Source - http://gecko.gc.maricopa.edu/~medgar/WinXPClassicLogon.html
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How to change the classic logon screen on Windows XP to use any fonts, colors, wallpaper, background, screen saver, et cetera.
These instructions can easily be generalized to change the logon screen for any desired theme.
HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\ThemeManager
DllName
value to %SystemRoot%\Resources\themes\Windows Classic.theme
HKEY_USERS\.DEFAULT\Control Panel
key (optional) HKEY_USERS\.DEFAULT\Control Panel
HKEY_CURRENT_USER\Control Panel
key HKEY_CURRENT_USER\Control Panel
[HKEY_CURRENT_USER
with [HKEY_USERS\.DEFAULT