When I shoot fireworks I tend to use the same methodology as when I shoot waterfalls. I setup the camera for 1-2" worth of exposure, ISO 200, and whatever F stop is appropriate (usually F16-20). The camera sits on a tripod and I do a manual focus to the general area the display will be in the sky. From there it is just a matter of timing my shutter presses (using a wireless remote) to try to get the best 2 second windows as possible. All of these shots were done in this way, and have minimal processing done in Photoshop.