Great article on Digital SLRs- Digital single-lens reflex (SLR) cameras are the standard tool for serious photographers. With the recent introduction of cameras such as the Nikon D70s and the Canon Digital Rebel XT the market for digital SLR cameras has expanded tremendously. A point-and-shoot compact digital camera can offer reasonably good image quality but a digital SLR, which usually looks a lot like an old standard 35mm film camera and may use the same lenses. Link.
Building a Digital SLR Camera System