function title {
  local tmp
  tmp=(${(f)*})
  printf "\e]0;%s\a" "${tmp[1]}"
}

case "$TERM" in
  (*xterm*|rxvt*)
    function title_precmd  { title "${(%):-[%n@%m] %~}" }
    function title_preexec { title "$1" }
  ;;
  (*)
    function title_precmd  {}
    function title_preexec {}
  ;;
esac

autoload -U add-zsh-hook
add-zsh-hook precmd  title_precmd
add-zsh-hook preexec title_preexec