A lot depends on which lenses you are shooting with and the camera's high ISO quality. The higher the ISO number, the better shutter speeds you can pull off without a flash. However, with a higher ISO number, the image quality will start to suffer with a lower end camera. The more expensive the camera the better the high ISO shots will come out (for the most part)
Also a faster lens (read, smaller f-number) will allow more light into the shot, however will also produce a small depth of field, and the background of the shot will be blurred out (which looks great in some shots, and is undesirable in others)
Play around with different ISO settings and see how shots turn out. You will need to put ur camera into manual mode to do most of this.
The best quality shots are going to result from using a flash mounted slightly higher than the camera on a bracket, or hand held with a cord controlling the flash.
You'll start to really enjoy messing with this stuff!!