FAQ: Disable/Enable Screen Saver

To disable the screen saver(SS) for the current user's session use:
SystemParametersInfo(SPI_SETSCREENSAVEACTIVE, FALSE, 0, 0);

For enabling, just set FALSE parameter to TRUE

Note: This only works for the current user in the current session. If the system is rebooted or the user logs off, the SS is reenabled.

I use this routine to disable my SS before writing a CD-R so that I don't have to either find my desktop and right-click or open the Control Panel, because both require you to change it back again!

P.S. For more info on the routine see MSDN:
Article ID: Q126627

Hope this helps...
Marc