set your premiere or vega timeline to work with 720p footage.
Nikon D90 shoots 1280x720 size videos, so if you put in 4:3 PAL sequence settings, you get top and bottom black bars (aka. Letterbox) if it does an automatic scale to fit.
If you put the Nikon D90 footage to a HD 1920x1080 sequence settings, your image will be smaller, thus you see black 'borders' around. You need to scale up your video to fit 1920x1080 or set your sequence to fit the Nikon D90 .mov footage.