Set your camera on "M" Manual
Set your Shutter on "B" Bulb
Set your aperture on the WIDEST OPENING.....Smallest # (f/1.8 for
example or with the Kit lens f/3.5
Set lens on "M" focus and INF and 17-25mm setting
USE ISO 800 or 1600 with Noise Reduction ON
Place the Camera on Tripod
Aim Camera at on the area of the sky where they are exploding and
lock it down.
Press shutter just before they explode, and release the shutter right
after they end. OR use a remote switch to open and close the shutter.
You may need to use a smaller f/stop (larger number: like f/5.6 or
f/8) Check your histogram highlights to set the proper f/stop if need)
Post some examples here.....be kind......400x600 or so
--
'Well, Good Luck With That' (SpongeBob SquarePants)
Well, Good luck with that indeed!
By and large that's reasonably good advice but I can't help but take issue with a few points. Neither a high ISO setting or a wide aperture would be adventageous unless perhaps the fireworks were going off several miles away somewhere behind a raging blizzard. These things are bright. So bright that it can be a challenge limiting the exposure enough to prevent them from blowing out entirely.
Shoot at the minimum ISO value. On the 400D, that would be ISO 100. Stop the lens down to about f/16 as a starting point. Sometimes you might want to open up a little bit wider in order to better expose any lighted areas in the background, etc. but not by too much. Depending on how close you are and how bright the displays are (and particularly during the "Grand Finale") you may want to stop the lens down even farther if possible in order to maintain good color saturation.
Some purists might insist that these smaller aperture sizes fall beyond the diffraction limit of the camera/lens. Fuhgetaboudit. You're shooting sparks spinning around a dark smokey sky under very long exposures. Diffraction will be the least of your problems.
With fireworks, you are essentially painting with light. The appearance of fireworks before our eyes depends heavily on our own persistence of vision, the same thing that allows movies to be viewed as continuous streams rather than an undecipherable collection of individual still images. Our cameras don't have this luxury so we need to keep the shutter open for at least a few seconds to allow the bursts to paint their way across the frame. That alone can let a lot of light in which is why small apertures are important. The combination of a wide aperture and a long exposure will result in overexposure, which in turn means blown highlights (colors shifting to white). They'll still look pretty good when overexposed this way, they just won't be very colorful.
A tripod is very important because of the length of time the shutter will be open. You can shoot hand held, but the results might not be quite what you're after. It'll look like a sort of "shaky cam" rendition of a fireworks show instead of looking like actual fireworks.
With the shutter in the B (Bulb) setting, the timing of when to open and then close the shutter can vary quite a bit. With a short bit of practice (chimping the LCD as you go) you'll be able to find the right rhythm. For starters, try opening up the shutter just as a report launches, keep it open through at least a large part of the burst before closing it. Two to three seconds is a common minimum, but (especially with a smaller aperture) as long as seven or eight seconds would be about max. Four seconds or so usually being a pretty good average. The effect will vary depending on the actual length of exposure. If you want to get fancy, juts keep the shutter open for an extended period and use something like a baseball cap to (carefully) place over the lens in between launches allowing you to capture two or more launches onto a single frame for a multiple exposure effect. If possible, stop the lens down an additonal stop or two when doing this.
Focal length will depend on how close you actually are, but unless they're right on top of you, you won't need a very wide angle setting. Having a medium range zoom lens available will help you to make quick framing adjustments on the fly.
If you can, try and include something on the ground and/or a horizion in the view to provide a point of reference. Turning the cameras long exposure noise reduction can help the appearance of the photo's a great deal, but it will slow you down as there will be a delay of a few seconds following each exposure before the camera will be ready for the next capture.
Have fun! And don't get so involved in shooting the show that you forget to enjoy watching it too.
Here's a couple quick samples taken in Chicago...
3.5 seconds f/16 ISO 100 70mm
9 seconds f/18 ISO 100 62mm
--
'Here, look at the monkey. Look at the silly monkey!'
Tom Young
http://www.pbase.com/tyoung/ 
