I just had a go at Mplayer... Very nice little program. Its ability to let me spec the precise aspect ratio and cropping of the movie file is very useful. I tried it when I ran into some frustration moments with both Quicktime and Windows Media Player, when I wanted to zoom in on a letterboxed video file (to remove the black bars on my 16:9 TV) and couldn't do so. A quick scan through the Mplayer command-line parameters and now I've got an icon onto which I can drag MPG files and it crops/zooms to the precise aspect ratio I want. Sweet.