How can I have zsh as my default shell?
Everybody on the system has to use bash as login shell, because this allows us to put a standard configuration into each account.
But don't worry, it's no problem to change the shell for all further operations after the login. Just put export SHELL=/bin/zsh into your ~/.bashrc or setenv SHELL /bin/zsh in your ~/.cshrc (in case you where not yet switched to bash as default shell and still have it set to tcsh).