Someone must really like you to give you a 20d! Color me a little jealous!
Anyways, my experience with the 20d and fireworks is this: when the camera records a long exposure (in my case the exposures were of more than 30seconds), the camera seems to take equally as long to save the image onto the memory card! Example: You snap a shot, wait 15+ seconds till you hear the shutter close and then wait another 15+ seconds while the camera saves the picture to the memory card. A little frustrating, but with a little planning, you can get some neat shots!
Long exposure time=cool streaky firework effects!
The settings I used on the camera are as follows:
"film" speed=100 ISO
Fully Manual (M),
Shutter speed=30 seconds(30")
Aperture= f18
and autofocus turned off. Pre-focus on something like the castle with AF if you'd like then turn it off. It worked for me!
Hope I haven't confused you with too many techie specs. yet!
As far as physical set up of equipment, I recommend a table top tripod and a park map or anything to cover up the lens while shooting.
As the fireworks go off, push the shutter button and let the camera do all the work. In between firework bursts, cover up the lens with the map so as not to over-expose the picture, and uncover for the next set of fireworks. With these settings I was able to get some decent shots. Unfortunately I can't post URL's yet but a few of my Disney fireworks pictures are at webshots and my username is the same as here: Puckfly.
Hope it helps!
John