I shoot in the same conditions on a regular basis using my old D70s, but with faster motion as I cover dance events and competitions. Let me tell you, it's very, very, difficult. You definitely want a recent camera which handles noise well such as the D7000 or the D700.
The key is getting a fast lens, a camera that handle luminance noise well, and always shoot in RAW mode because you'll need the extra color information in post when adjusting exposure. Chroma noise is easy to handle, so don't worry about it. The F1.8D 50mm is a good lens for this type of work, and it's conveniently cheap.
One of the keys to shooting in low light is you need to control the shutter and aperture yourself. If you let the camera do it, you'll get a lot of undesired and unexpected results. For example, if you use the program mode (P), Nikon tends to favor raising ISO before adjusting shutter speed or aperture. On older cameras like my D70s, it has absolutely horrible unusable noise for anything shot above ISO 640. for some shots, simply opening the aperature one stop or slowing the shutter down would capture the image appropriately, but if left in program mode, the ISO will max out before shutter or aperture are adjusted resulting in needlessly noisy images. Better to under expose with clean ISO than to expose properly with a higher noisy ISO setting.
Typically I start with aperture fully open at F1.8, set ISO at 400, then start with shutter speed around 1/100th of a second. I'll take about 30 or so warmup shots around the venue then view the results. If they're too dark, I slow the shutter down to 1/60th then raise the ISO to 640. If it's still too dark, I slow the shutter down a bit more. But that's as far as I go because you can brighten an image about 1.0 EV in post before it really starts to break down. At some point you have to limit motion blur - not just from people moving around, but also from your own body movement causing camera shake when you press the trigger. Practice breath control when shooting as it doesn't take much to ruin a shot.
One of the first problems you'll run into is difficulty focusing. Many cameras use contrast detection to focus the image. In low light there isn't much contrast because there's less distinction between bright and dark. Manual focus will also be tough because the viewfinder will be too dark to see through in some cases. You'll have to train yourself to pay attention to small areas of contrast in the frame (such as the rim/silhouette edges of a person) to obtain a focal target to compose your shots. I've lost many shots because my camera's autofocus was fooled into focusing on the wrong details or was in the middle of re-focusing when I wanted to pull the trigger. One strategy is to zoom out / stand a little further from your subject so you can focus on a constrasty part of the frame for focus, then crop in post so you get the composition.
Another problem with low light is small depth of field. At F1.8 in low light, you're looking at a depth of field of only a few inches at most. So your focus has to be spot on to get a quality shot. Otherwise get real familiar with your unsharp mask tool in your favorite photo editing software. Make sure the subject of attention is the focal point. In the case of dancers, it usually means only the guy or the girl gets in focus while the other is slightly blurry. If you aim for the shoulder to get contrast, it's possible the face will be out of focus if the dancer is leaning directly towards or away from the camera.
As for color - low light shots tend to come out over saturated and too red/orange. i frequently have to de-saturate and adjust the color temperature. I've tried ajusting white balance in camera as well as post. In post seems to be less hassle.
Finally, one of the perks of shooting low light is interesting light and color interaction. Using a flash tends to wash all this away and creating boring shots. So try to go flashless if possible and pay attention to shadow as well as light. going flashless will also provide more freedom to move around as you won't be announcing your position with each shot. Dancers tend to tighten up in the presence of cameras (go figure) as they feel like they have to perform for an audience rather than just have fun dancing. Shooting incognito gives you access to those nice unscripted nuances.
