Thanks! I found another way, from the command line (as root):
niutil -createprop / /users/username shell /bin/bash
Now I've compiled Bash 2.04 for OSX, and posted it, instructions on how to install it, here:
I have one problem - when I start a new shell from the Terminal program, Bash runs /etc/profile, but when I su, it doesn't run it and defaults back to its default appearance, prompt, etc. I haven't figure out where to put bashrc to make it initialize each time.