splicing togeter avi's

I have figured out how to splice avi's together using Pinnacle Studio. However once the avi's are loaded into that program, the pictures are "squished" to fit the screen. This results in a distorted view of the avi. I assume this is because the size of the avi I am saving in Morpheus is not a standard size? Any suggestion on how I can work this so that the avi's are not "squished" or "stretched" out of proportion?