One of the things I regret about my education was that music classes and choir in school never really taught anything about the voice. The focus was entirely on the songs, not the singers. I learned a bit about the music itself, but not how to sing it.

Perhaps you could find someone who can come to choir practice and put on a voice seminar. I don't mean they can be taught a lot of fancy classical stuff in such a short time, but just some basics about throat and chest relaxation and support, including how to breathe. The breathing bit can make a dramatic change, and is relatively simple for a good teacher to get accross.

See Threads on the Singing Voice. This thread was started by Alice to provide links to all the threads where the art of singing was discussed.