Donn Lee's blog

Restrict the Screen Saver (Windows 2000/XP) at Registry Guide for Windows:
"Create a new DWORD value called 'ScreenSaveActive' and set it to '0' to disable all screen savers.
Alternatively create a new string value called 'SCRNSAVE.EXE' and set it to the executable name of a valid Windows screen saver file, including the .scr extension. This will only be used if 'ScreenSaveActive' is set to '1' or deleted from the registry.
Restart Windows for the change to take effect.

Registry Settings
User Key: [HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control PanelDesktop]
Value Name: ScreenSaveActive, SCRNSAVE.EXE
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disable screen savers, 1 = default)"

Disable the Lock Workstation Button (Windows NT/2000/XP) at Registry Guide for Windows: "Registry Settings
User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\PoliciesSystem]
System Key: [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\PoliciesSystem]
Value Name: DisableLockWorkstation
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disabled, 1 = enabled)"