John - I used the same settings on my D50 - got about 30% decent shots - and about 5% (maybe at best) ok shots - and a few great shots

seems hit or miss with them - I did what you did with opening the shutter as I heard them go off - then as they reached their biggest diameter without dissipating yet i closed the shutter - I tried a few 15-20 sec exposures but found that since most of the fireworks were in the same area of the sky i got alot of blown out white areas - so i tried to limit the exposure to 2-3 at a time

here is one that stood out to me so far - there are maybe 2 more that just stand out as decent