Hello Ali,

Unfortunately there is no way to change the Windows logon screen without the use of third-party programs.

In Windows XP, the logon screen is referred to as the Welcome Screen. The GUI elements for the Welcome screen are housed in the logongui.exe file in your System32 directory. Since this is a compiled file, the only way to edit it is through the use of some third-party program such as Resource Hacker....

As you probably well imagined, these settings are held in the registry. Specifically, file type handlers are housed in the HKEY_CLASSES_RO OT hive. If you navigate this hive in the Registry Editor, you'll notice a key dedicated to each registered file type on your system. So your .xml settings will be housed here:

HKEY_CLASSES_RO OT\.xml

This key is used to register the file type and its handler along with any other...