Seriously, you can do this in System Preferences, in the blue apple menu in the upper left corner of your screen.
Once opened, just type hot corners and you'll notice a few possibilities, such as Exposé and also the Screen Saver. The Screen Saver preferences actually just has a button that sends you to the Dashboard & Exposé preferences. In there, you can set whatever each corner should do, or choose the "-" for nothing at all.
thank you unfortunately that's where our hot corners are set, to the - sign and the **** things keep vanishing the screen when we move the mouse about. i don't know why it doesn't recognize the setting.