OK, here goes.
After you import the file, right-click on it and select Interpret Footage. There are 2 options that affect your problem. One is "Use Pixel Aspect Ratio from File", the other is "Conform To".
If the first option shows D1/DV PAL Widescreen 16:9 (1.457) then it is correct (assuming your file is really widescreen).
If the first option shows anything different from the above, select the second option, and from the drop-down list, select D1/DV PAL Widescreen 16:9 (1.457).
You may think that 720x576 is 4:3 aspect ratio, but the Pixel Aspect Ratio, which you should set as above, also affects the way the video appears. For DV files, 4:3 and 16:9 have exactly the same resolution (720x576) but if the file is set to widescreen, the pixels will be stretched during playback. Pixel Aspect Ratio of 1.457 means that the pixels are almost 1.5 times wider than they are tall, which is why the video looks widescreen.
Good luck!