Astrophotographers, please help..?

Buy a more expensive lens. The Canon Rebel XTi is an overall great camera, it's about what you do with it. The kit lens is a piece of junk, and I'd recommend researching a bit more and getting a good telephoto or portrait lens. Also, when my boyfriend had one, he always raved about wanting a flash for it. I don't think it's entirely too necessary, but it does improve lighting a bit. Practice more with it and you'll improve.