What you need is a DSLR and a external flash. The ultimate in low light work would be a 5D, a 580EX flash, and the 24-70mm f2.8 lens. (At least in the canon world. I don't keep up with Nikon). Of course, that will run you about 4k, and many people would (correctly) tell you that you need an "assortment of fast primes" to really have the best low light setup, but that would inflate the budget even more. So, assuming 4k is more than you want to spend, you need to see where you can cut corners. The 5D is a better low light performer than the rebel XTi, but it's unlikely the difference is worth it to you. If you go with the XTi, we can "sidegrade" the lens to the 17-55mm f2.8 IS lens, which is an amazing lens, still costing about 1k. The 580EX is better than the 430EX, but not by much. Are you trying to fill an auditorium with light, or a board room? A board room or smaller, you won't notice the difference, so get the 430EX.

So, now are costs are approximately 700 for the camera, 300 for the flash, 1000 for the lens. If 2k is too expensive, start paring down that lens. The 3rd party manufacturers (sigma, tonkina, tamrom) make nice 18-50ish f2.8 zooms. Buy one of those for $400, and your cost is around 1400. No image stabilization, but a solid performing lens indoors. $1373 total at BH, spend $40 on a pair of 2GB CF cards, and you'll be all set.

That's where I'd end up if I were in your position. Nikon people can do a similar exercise, I tend think of Nikon as being a bit more expensive and a bit behind on the development curve, but Nikon people will cast similar aspersions at Canon. Canon also has a huge percent of the market, so the used market is especially vibrant, to the point where I never lose money buying and selling used lenses.

Matthew