I bought the XTi in december. The kit lens is ok (I have the non IS version). It's good for starters, but only for that. If you want to get the most out of your camera (whichever you choose), you'll need another lens. One big plus of the kit lens is that it's cheap and once you take a couple hundred shots with it you'll start to see which focal lengths you use the most and you can plan a lens purchase based on that.
As for the 100mm f2.8 macro, it's awesome!
Incredibly sharp, and since I got it I've used the kit lens only about 3 times. Keep in mind that 95% of my pics are macros, though.
It's great for portraits, but you have to be pretty far away if you want to get anything besides the head in the pic.
Also, for macrophotography, the depth of field is very narrow, so you have to stop down a lot to get some DOF. Also, since it's a 100mm lens, you need a high shutter speed (at least 1/100, unless you have a tripod) to get a sharp pic. That means you either have to have excellent lighting or use a high ISO. I do mostly field work, so I normally don't have good lighting and I don't like to use a high ISO, so I bought myself a canon ring flash (MR-14EX) and I couldn't be happier! you can check out my gallery if you'd like to see some pic with the 100mm macro and ring flash.
If you have any other questions regarding the 100mm macro, don't hesitate to ask