Making Before and After pictures?

I love when you can see the before and after in one picture. How do you make them? Is it a special program? I tried to make some in photoshop last night but the size of the pictures kept distorting the images - even if I hit the "shift" key during the sizing of them - which is supposed to keep them proportional.  Very frustrating.   Any suggestions on programs to use? I appreciate your help!!

I use Paint Shop Pro v7 to do my photos.  

I don't have photoshop, but I do have Microsoft Office, so I do mine in PowerPoint. If you insert the pictures on the slide side by side, then "save as" a JPEG, you should have a picture. If you leave the white of the slide showing, your picture will have a white border. But you can open the picture in Microsoft Office Picture Manager and crop that off. Not sure if this will help you or not, but it's how I do it. PM me if you need more instructions.

Good luck!