I am stepping up into the world of DLSR from P&S. It is my understanding that it will be better to buy a less expensive body, and use the saved money for a better lens. Hence I'm looking at the Canon Rebel XTi / Nikon D40x range of cameras (entry / prosumer level DSLR). Here is my question: How do I know what a good lens is? I know that "good" depends on what you want to do with it.... but what's the difference between the kit lens other lenses? Would any lens be better than the kit? For example, the kit lens for the XTi is a (EF-S 18-55mm f/3.5-5.6). Is the only difference between this lens and a more expensive lens the zoom and f-stop? Or are they better quality in another way? Are they made better? I'm just trying to learn here. FYI, I will be doing mostly portrait, landscape, maybe macro type stuff. Thanks in advance, I appreciate your input!