Right just got home and had a look, the way to do it, is to add a mask, do this by right clicking in the timeline area and selecting new > mask, the mask will then be added, then in the drop down for the new mask effect, there will be an option called mask shape, enter the pixel dimensions for the area you want to crop and click ok, that should do the trick, then just export the movie and the cropped parts won't show up. Hope that's what you asking for help on?