if you camera does indeed have a way to set the shutter speed, it's commonly represented by the letters "Tv" i'm unfamiliar with teh particulars of you camera, but if these letters appear on the mode selection dial on your camera, then flick it over to that. that will allow you to set your shutter speed, and you camera will take care of the rest of the details.
hope that helped.
actually after looking
here, it seems as though your camera has a 'manual' mode, using the camera in this mode should allow you to set your shutter speeds.