The best way to photograph storms or clouds is to use a digital camera and a tripod. Film does not capture as much detail as the digital camera does and with more and more companies making digital cameras, prices for these are falling rapidly. This is not the case though if you have a film SLR camera as they can capture more detail than digital. A recommendation for a digital camera would be at least 3 megapixels. I would personally recommend either Canon or Nikon as they have a very good reputation with the digital camera market.
Capturing storm structure is quite easy, just set up the tripod, put the camera on it and zoom into the area you wish to photograph. The only thing you need to worry about with doing this is the amount of sunlight present. You might have to adjust the exposure compensation on the camera to make the picture a little darker so it doesn't over expose the detail on the cloud.
This is an image that has been over exposed, you can see the loss of detail and the white wash look that the picture has.
This is a similar image taken 10 seconds later using an exposure compensation of -0.6 which has removed the white wash look.
Under exposing can be quite useful for sunset images as it tends to bring out the best of the colours in them
|Under exposing an image tends to bring out the deepest colours
This is a sunset picture taken of a storm using completely automatic settings. Note how the pink is not a vivid colour.
Lightning is one of the most difficult pictures to take because of its randonmess. The settings I use for lightning capture at night is a shutter speed of 8 seconds, aperture of F2.8 for lightning a fair distance of F8.0 for close lightning. The ISO I use is ISO 100. Below are a few examples of lightning capture
Lightning off Byron Bay
Close lightning (Aperture of F8.0)