Helicopters are great as a photography platform, it is possible to get an exceptional view. Try to get the pilot to fly with the doors off, as it will allow you to photography without looking through windows and gives a far better view. Photograping through the windows will give great loss of contrast in the images.
In general for aerial images, there are several main factors to be aware of. When taking images through the windows of aircraft the window material appears to be very dense and of poor optical quality, the images will loose quite a lot of contrast, however this can be overcome with digital images to some extent by post processing in Photoshop and giving the contrast a boost.