Thank you Mark! Yes, I use flash at meets except during the start where a strobe light is used by the offical. My equipment is the Canon 20d, 580ex speedlite and the canon 70 - 200 2.8 non IS, f3.5. I have found the mode that is best to shoot at indoor pools is AV and as I push the limits of the camera to achieve higher shutter speeds the ISO's are set to 3200. Yes, I could change the apperture to 2.8 to reach even higher speeds but then I loose in tack sharpness.
Other than that try to get low. The best is laying on the ground, but it's very wet and lots of swimmers and officials are walking back and forth so it doesn't always work.
I'm glad your going to try shooting swimming. I've got a question for you, have you shot hockey?