You need to set the printer properties. Go to printer properties and change the document size. You can select custom document size according to your desire. Secondly you can select the image size of your picture from your software. I advise you to use Picassa or ACDSee software for printing the pictures.
Mspaint - Free with windows - works just fine. You can resize the pix and you can also, in page setup, select "Fit to 1x1" or 2x2 or whatever. 1x1 is one whole page.