Preventing the Logon Screen Saver from Launching

Start/Run/Regedit

"HKEY_USERS\.DEFAULT\Control Panel\Desktop"

Value Name: ScreenSaveActive, Data Type: REG_SZ (String Value), Value Data: (0 = disabled, 1 =enabled). Change the value of 'ScreenSaveActive' to '0' to disable the screen saver.

Restart Windows for the change to take effect.

Note:
Windows has a default screen saver called login.scr, which runs even if no screen saver has been selected.