The logon bitmap is really a dialog that is part of GINA (Graphical Identification and Authentication). It handles the authentication for logging onto the system. If you want your own dialogs to appear, you need to write your own GINA handler. It's certainly not something for the feint of heart. There's not much documentation and you need to be intimately familiar with debugging through OS startup with WinDBG. It's definitely doable. If you have ever seen one of those biometric hardware devices, they have to replace the default GINA. For more information on the GINA and how it fits in the overall scheme of the operating system, see Russinovich's and Solomon's "Inside Windows 2000 Third Edition."
This was first published in April 2001