Hi everyone, After having used compact digi cams for a long time--such as the Canon Powershot--I am really interested in upgrading to a camera that can create higher quality photos. I always love that D-SLR's almost seem to produce a film quality look to the photos--it just seems to give the photo more importance and more weight. Similar, I suppose, to watching a movie shot on film as opposed to one shot on video. Anyways, while I am interested in reading reviews for certain models, I also just plain want to learn more. I'm seeing 100 different kinds of lenses for each model, but I don't even know basic things like what 75 to 100mm means in terms of focal length of a lens. And how that differs from another focal length, or when you would choose to use one lens over the other. I'd like to learn more about ISO, and really a bevy of other things as well. I'm sure I'll want to purchase a book, but at this point, can you guys point me in a direction to read some things online about D-SLR's that can break it down in layman's terms? Also, just a quick question...say one buys a Nikon camera. Does one need to buy a Nikon lens(es), or does buying another company's lens work (and work just as well)? Thanks in advance!