Yeah, to take really great photos of games at night under the lights or indoors in gyms... unfortunately it takes thousands of dollars in gear. You can still take decent shots with what you have, especially if you're allowed to use flash... but in general those low-light + fast action venues are the realm of full-frame sensor DSLR's and fast aperture (usually high dollar) lenses. It's all about getting the most light into the camera, and having the best high-ISO sensors to maximize what gets in. That usually means the bigger the sensor in your camera, the better. I have a 5D Mark III and several f/2.8 or better lenses and it's still a challenge.
One thing to try, I've done this with my (G11 with some success) is to shoot either in Av or Manual, and set your camera such that your shots are a little (1 to 1.5-stops or so) underexposed on purpose to keep a decent ISO (around 800 on my G11) and fairly fast shutter combination. In post processing (I use Lightroom mostly, but any decent editing software will probably work), I'll boost the exposure and try to minimize the noise as much as possible. Even then, you won't be able to make any huge enlargements out of it, but you can probably get some decent screen images and/or small prints.
