Dan Mitchell , Jan 11, 2008; 12:05 p.m.
In general, I recommend that latter approach - get the XTi with the kit lens now and hold off on additional lenses until you've shot a bit with the kit lens. After doing that you'll have a much better idea of what your eventual lens preferences might be. You'll still be able to get the same or other lenses at great prices if you look around a bit.
One alternative to think about might be to get the XTi body only and separately purchase the newer version of the 18-55mm kit lens which has image stabilization (IS) and is reportedly quite a good performer optically, especially considering the list price of less than $200.
While you could invest in other more expensive options, until you are pretty sure what those might be - and that takes a bit of shooting to figure out - it may well be better to stick with the one lens.
The EFS lenses are designed for use exclusively on Canon's crop sensor DSLR bodies, including the XT, XTi, 20D, 30D, and 40D. The lenses are designed a bit differently - they extend further into the body of the camera and generally throw a smaller image circle onto the smaller 1.6x cropped sensor. These lenses will work only on the crop sensor bodies; they will not work on full frame bodies like the 1 series or the 5D. There are some excellent lenses among the EFS series, in particular the 10-22 ultra wide and the 17-55 f/2.8 IS. At some point, it is even possible that you'll decide to add one or more of these to your kit.
Another note: questions like yours almost inevitably get one or more replies that say "go and by the Canon 50mm f/1.8 lens," either as the only lens or as an adjunct. Unless you are a bit unusual, I'm going to recommend - strongly - that you also resist that advice. I will concede that the 50mm f/1.8 is a fine piece of glass and that it sells at an amazingly low price. However, it is generally the wrong lens for someone starting out with a new crop sensor DSLR kit. I won't go into the reason for saying this right now, but I'd be happy to explain if you want me to. (It could be a good choice later on if, for example, you need a short telephoto portrait lens.)