[CentOS] adding x to an existing system

Hello,
    I've got a centos5 box that originally did not have x on it as it was 
headless. It's purpose has now changed and x is now needed. I'd like to 
install it and gnome preferably without having to reinstall the os to get 
the ease of install, it just works when anaconda does it, is this doable?
Thanks.
Dave.