If you really want to run Linux then the best idea is to go and install Linux. That is the only way that you are going to really learn the system. There are many online forums and IRC chat channels dedicated for helping people with their questions about Linux my personal favorite is LinuxQuestions.org where you will find hundreds of Linux users. Also don't forget that there are many man pages already on your Mac for many commands just open up the terminal and type 'man [command]'.
I am a UNIX major and can help with any questions you might have. What is your goal? Are you wanting to run Linux or UNIX (FreeBSD/Solaris?) as a server or as a workstation? Depending on your goal will depend on what you will want to install. If you have a spare computer or two I suggest trying out several distros of Linux or some of the various flavors of UNIX till you find something that you like and that does what you need it to do. As for books, that will depend on your goals as well. However, don't purchase a book if you don't have to, since most of the stuff is already in the man pages or online. Experiment and you shall go far!