I was able to import an avi (MJPEG) video file of 90 seconds to AE. The duration is listed in the project files window. However, whenever I bring it to the composition window, I am only able to see the first 30 seconds or so.
I am an AE newbie, but experienced with Pinnacle. I can't figure out how to expand the avi to its full duration, or even to select a different 30-second segment of the video in my composition. If you answer, consider yourself to be awesome.
When you import the video the entire video is imported. When you create a new composition the length is automatically set to the length of the last comp you created. You can change the length of the composition with the composition settings (Ctrl/Cmnd + K or Composition>Composition Settings)
If you have no composition open, no timeline visible, you can drag an imported video into the empty Composition Panel and AE will create a new composition that is the same length, size, pixel aspect ratio, and frame rate as your video. You can also select any asset in the Project panel, right click and select Create Composition from Selected or drag the asset to the New Composition icon at the bottom of the panel.
All of these techniques are basics. If you are new to AE you should go through the getting started materials available here. You can also get some great info and great pointers by simply typing a short question in the Search Help field at the top right corner of the app window.