First of all how important is IS in a lens for a beginner. Will it help me shoot with much ease or just a feature that I will hardly use or know how to use fully. Second, between the 2 lenses below, which one would you suggest for a complete noob to start with. I'd rather get the Sigma but it doesn't have IS which I'm not sure if its necessary when I shoot. http://www.adorama.com/SG1770EOS.html http://www.amazon.com/Canon-EF-S-18...1?ie=UTF8&s=electronics&qid=1202836861&sr=8-1 btw these are going to go on a Xti. thanks for any suggestions.