I've had a few people tell me that the cards on the print sheets have been coming out the wrong size. If you're having a problem printing, tell me what's going on in the comments to this post.
The cards on print sheet should be exactly the size of a normal Magic card -- 88 mm along the vertical axis -- at 207 pixels/inch. The files are meant to be printed on standard letter-sized paper, with margins of 0.5 inch on each side. Make sure your printer is not set to resize when you print.
If you need a program to print .jpg files, I recommend GIMP, which is kind of like an open-source version of Photoshop. It's what I used to make the print sheets, so it should work for you. You can download it here.