Even at 100% of scan it should be no bigger than A4 try it at 800x600 to see if it is more manageable and increase the size to suit your needs.
My 17" TFT has a screen resolution of 1280X1024 pixels, now that is huge well over A4 size check your screen resolution, hold up a piece of A4 and it will give you an ides of what the resolution should be.
Can your Imaging software not do an image capture, import using a twain device (e.g. your scanner), that should give you more control once you have imported the data.
I'm shutting down for the night now, that should give you something to be getting on with.