Hi there,
Do you happen to have Photoshop Elements or the like that came, perhaps, with your scanner? If so, it's really easy.
Open one image, do an Image Resize (whatever it may be called in your app) and resize it 200% horizontally, making sure your original image stays flush to the left (or right); usually there's a 9x9 grid letting you specify where you want the original image placed in the resized image. Then open the second image, copy & paste onto the first one, and align. When priting, select "Fit to paper" and you won't have to worry about resizing it.
If you don't have an app that can do this, I recommend The Gimp, which is a freeware alternative to Photoshop. Little bit of a learning curve to it, but for what you want to do, it should'nt be that bad. If you're willing to spend a little money (but not as much as for Photoshop or Elements), then GraphicConverter used to be my fave.
Personally, I got a russian stereo adapter for my Helios-44M and shoot with that :-)