The trial version does not support mpeg formats of any kind. I’m guessing your AVI file uses an mpeg based codec. Use a utility like GSpot to determine the codecs used in your AVI files.
You will also find links to many free tutorials in the PremiereProPedia that will quickly show you how things are done in Premiere Pro.
The “source view” has several purposes, but is intended for working with a specific clip, while the “program view” shows you what your timeline contains.
You will find links to many free tutorials in the PremiereProPedia that will quickly show you how things are done in Premiere Pro.