From my exp, nearly every gym is pretty dark. I shot tens of thousands of frames a few years ago in a gym with a 30d- at 3200, 100mmf2- af f2, and i don't hold me to it, but i think i was in the area of 1/500, or a bit slower. Technically they would now be considered a mess, but at the time they were pretty good, and a far cry from what the people in the stands could do with point and shoots.
Like most things, it all depends on what you are required/want to do, and how much you have to spend. Good looking high iso cameras are fantastic, but if you can use a flash of some sort, it'll be even better. For basketball, i would look into 1 or 2 alienbees monolights, battery packs, triggers, and some sort of clamping system or maybe stands. just be very careful with you're placement, and i don't mean just for lighting. you really don't want anyone getting hurt due to your equipment.
On second thought, what you really need to do is buy a large speedotron pack with whatever heads you need to get you to the flash duration you want. Then you just need a scissor at the gym to lift it all up in the rafters, with everything triggered wirelessly. just like they do at NBA games! just make sure EVERYTHING, is VERY well secured. if a "head" was to land on someone, it would be a trip to the hospital at least, a falling powerpack would render someone dead on the spot. (powerpack = a large car battery)