I am using Video Pro X. when I import 1920 x 1080 avi files they have an aspect ratio of 4:3 instead of 16:9.
The unedited files play as 16:9 on windows media player.
If you get a file where the aspect ratio isn't detected properly, just right-click on the video track (in timeline mode) after importing the file and go to "Object properties". In this dialog, you can adjust the aspect ratio manually.