About to Buy a Canon Rebel XS, Please, need advice on Lens! ?

IF that is what you want, then go for it! You are going to find that telephoto lenses are not nearly the fun you think they will be, but if you want to learn to use them, go for it. Just make sure you have a standard 18-55 or so lens (18-100+ is a great compromise...remember, with digital, all mm lenses are almost 1/2 again their focal lenght as film cameras...and the steadiness in which you hold a camera becomes critical when shooting long lens shots! IF the telephoto lens is not image stablilized, you will need to shoot at about 1/1000 second in hand held using a 250mm lens!!!!