When you disable fast user-switching in Windows XP and don't use the icon-based login screen, you log in with the old-school text box, which asks for your user name and password.
As I'll demonstrate on the show, you can change the text in this box from "Enter a user name and password that is valid for this system" to "Get your stinkin' hands off my computer." Or perhaps to something sweeter, such as "Marry me, Doreen, I'll get you a new GeForce if you say yes."
You could use this trick in a public setting to inform users of the proper policy for logging in, such as, "Please see an attendant for login information." It's a quick registry hack. Just follow these steps:
1. Start the Windows XP Registry. (Go to Start and then Run. Type "regedit" without the quotes. Hacking the registry can be dangerous)
2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon.
3. Create a new String Value named LogonPrompt and set its value to whatever you want.
Now your computer truly reflects your personality. You can keep the key bookmarked to go back and change it whenever you're feeling particularly creative.
The above article was taken from TechTV.