Applescript to disable screen saver through sending keystroke
Check out the dictionary for the System Events app that's included with Applescript. You can access it from the AppleScript Editor:


  File > Open Dictionary... > System Events.app


There's a class called "screen saver preferences object" in there that should do what you need without having to script the GUI.

EDIT: Try setting the property "delay interval" of the object to 0 to disable the screensaver.