dSLR. Is this a good buy: Canon Digital Rebel XSi 12MP Digital SLR Camera with

Amazon is a good, legitimate site, I wouldn't worry about ordering through them. The Canon you are looking at is the newer version of my 10mpx Rebel XTi, which I absolutely love. I upgraded to my Canon after practicing with a Pentax SLR film camera. The Nikon D80 is a very nice camera, and would be an awesome starter - the only reason I liked it less than the Canon is b/c I have small hands and the Nikon just seemed huge when I held it. The 18-55 lens is a good starter, 55mm is standard for general photography. In order to get great pics, you'll want to read up about f-stops, aperture, shutter speed, and depth of field and really understand how they work in order to fully understand how to operate your camera.
I think you're looking at a pretty good deal on that Canon, and Amazon should be scam-free. I wouldn't order from a random company or a place like ebay for a camera - that's where you'll get had.
Canon and Nikon are both professional quality cameras - you'll love whichever one you get!!