If you’re ever in the need to keep users from changing their screen saver, for whatever reason, follow these steps:

Go to START, then RUN. Enter this command: gpedit.msc
This opens the local system policy, and you’ll find the options you require under:
Local Computer Policy > User Configuration > Administrative Templates > Control Panel > Display

Then change the following four options to set a specific screensaver and lock it:

• Change the option “Screen Saver” to Enabled
• Change the option “Screen Saver Executable Name” to Enabled, and enter the file name of an .scr file (from the Windows directory) in the box labeled “Screen Saver executable name”. For example, to set the screen saver to the logon screen saver, enter “logon.scr”.
• Change the option “Password Protect the Screen Saver” to Enabled (to password protect the screen saver and lock it) or Disabled (to keep password protection from applying to the screen saver and lock it), as necessary.
• Change the option “Screen Saver Timeout” to Enabled, and enter the number of seconds in the box labeled “Seconds”. (10 minutes = 600 seconds)

This will lock changing the screen saver, and set the screen saver options and lock them from being changed.