I paid a nice chunk of change for my dSLR (Canon 20D - big brother to the XT), but the lenses are definitely the expensive part. Right now I have about $1700 in lenses, but there are a couple lenses on my wishlist that are over $1k each....so yeah, top quality lenses are expensive. But oooohhh so nice to use.

Though there is definitely a lot to be said for getting a nice lens with a nice big max aperture (2.8 or lower), I should mention that the Canon Rebel XT has very good noise characteristics, and even at 1600 the picture is definitely usable (and with a little noise reduction can even be enlarged fairly well). I shot a friend's wedding almost entirely at ISO 1600 (indoors, fairly low light with a rented Canon 24-70 f/2.8L lens - what an amazing lens!) and the results were actually surprisingly good (shameless link ).

ISO 800 is even better (in terms of noise), so you may be able to get away with the zoom Mark suggested and never straying below ISO 800. But in many cases even ISO 800 at f/4 or f/5.6 will only give you shutter speeds around 1/60 indoors, which should be enough to get a decently sharp shot with a little motion blur, but only if you've got steady hands and are shooting at the short end of the zoom. if you're shooting at the long end of that zoom, then it's going to take statue-like steadiness to get sharp shots - or you'll have to shoot from a tripod.

I would actually highly recommend the 85mm f/1.8 - I have it myself and it is really a fantastic lens - one of the best deals out there for Canon in terms of image quality for the buck. It's very sharp, focuses quickly and silently, and the f/1.8 is just fantastic for low light shooting. For the price it really can't be beat, and if you can get moderately close to the pool you should be able to get enough reach to not have to crop away too much of the shot. The effective focal range would actually be about 136mm and assuming you're not in a huge aquatic center that should get you fairly close (the XT's sensor is smaller than a regular 35mm frame, so the field of view we get on the picture is about 1.6x the focal length of the lens).