It's hard to tell with such small images, but it appears you are off to a good start!
Originally Posted by George Riddle
There are some interesting aspects to photographing fireworks that you can use on your next attempt. First, you're apparently already using a tripod, and probably have a remote trigger device for it. Obviously you are using manual exposure settings too. I can't tell if you turned off auto focus or not, but manual focus an absolute requirement.
Then consider that, because the fireworks moves, shutter speed has virtually nothing to do its exposure! ISO settings and aperture control exposure of the light from the fireworks. The shutter speed controls how much of an explosion is included... plus how much exposure any surrounding background gets.
With a D70 you'll want to look at a histogram or the blinking highlight display after an initial shot to see if the fireworks is being over exposed. It's probably best to keep the ISO as low as possible, and then keep the aperture in the f/8 to f/16 range. F/8 would be preferred for sharpness, but even at ISO 100 may overexpose the fireworks too much.
This image was shot at ISO 200, f/14, and 8 seconds exposure using a Nikon D3 with a 28-105mm f/3.5-4.5 lens set to 60mm.