Found this in the MS KnowledgeBase, at this URL: http://support.microsoft.com/search/preview.aspx?scid=kb;en-us;Q314493 Change the Logon Screen Saver To change the logon screen saver, follow these steps.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk. Click Start, and then click Run. In the Open box, type regedt32, and then click OK. In the Registry Editor window, locate the following registry key: HKEY_USERS\DEFAULT\Control Panel\Desktop In the right pane, double-click SCRNSAVE.EXE. In the Edit String dialog box, type the name of the screen saver that you want in the Value data box, and then click OK. For example, if you want to use the Mystify screen saver as your logon screen saver, type ssmyst.scr. IMPORTANT: Make sure that you correctly specify the path to the screen saver. If the screen saver is located in %SystemRoot%\System32, the explicit path is not required. Click Exit on the File menu to quit Registry Editor. The logon screen saver changes to the screen saver that you specified. Visit the URL and it also tells how to do it in Win2000, and how to change the tiemout, and even how to totally disable the logon screensaver.