I am trying to get some advice on shooting girls basketball...indoors. I have a Nikon D70 with a 70 - 300 Sigma Lens 4-5.6 No VR, and a 18 55 Kit lens 3.5-5.6 with VR. So far I have tried lighting to Auto (which seems to look fine) ISO set to Auto (which works fine..I can always clean up a bit of noise). What I can't seem to get is the correct shutter speed to capture as little blur as possible with flash. My latest was shot at 1/125 at 5.6 Iso Auto, WB Auto. Any suggestions on how to get the most out of what I already have?

I don't know that much about it but I would imagine your biggest problem is going to be lighting. Unless you are shooting at a venue with very good lighting your shutter is always going to have to stay open longer than it would it sunlight to get a decent exposure.

Try shutter speed priority (S, highest passable ISO (1600? 800?) and try your shutter speed of 1/125. also, try getting closer to the action, needing less zoom, and allowing the lens's aperture to be wider (f4 @ 70mm). That ought to get you at least in the right direction.

You know what Paul - indoor sports sucks for the average Photographer because there are so many elements that are out of your control. Especially in a Gymnasium, there are now additional rules to follow like No Flash! or you have to stay in your seat, dont block someone elses view. Then you quickly discover, if you do try to get quality photos, you dont have the right equipment to produce them.
So lets look at what you can control: in most gyms the lighting is OK but not ideal, and your lens may not be fast enough to take it all in. Based on an average Gym, you would ideally need a lens with a F2.0 of better. In most Gyms, Flash photography is not allowed, because you may momentarily blind the player. So I would say that a good lens is your top priority. The ISO could be cranked up to a minimum of 400, but all this will still produce blurred images unless you use the aid of a good tripod or monopod. If it were me, I would set my focus to manual and follow or Pan the player and anticipate where the action will be, then snap the picture. Thinking ahead is mandatory and then follow Robs advice of getting closer to the action. The less zoom, the more available light, the more action the more possible blurr, plan your shots for that momentary freeze in action. Always pre-check your white balance, and use a filter to compensate for the yellow light reflected from the Gym floor.
Based on the information you have provided about your equipment, you lens just doesnt let in enough light, so get closer to the action, plan ahead, and a shutter speed of 1/125 or 1/250 should work well.