Though many people have many different views on what a hacker is, and what a cracker is, here's what I've heard (by far) the most: A hacker is someone who can program, knows the internet, and knows operating systems. They generally use this knowledge for good, or personal experimentation. A cracker is someone who uses that knowledge (or someone else's script [fucking script kiddies]) in a purposefully malicous manner. They're also refered to as White-Hat, and Black-Hat hackers, respectfully.
That said, one of the all time best books for learning your stuff is "Maximum Security: A hackers guide to protecting your internet site and network". It's easily over 800 pages long, so it'l take you a while.
I also suggest you look around on the web. There are some great tuts out there. The best way is also, if possible, to set up your own network and hack into your own machines. That way, when your still a n00bie, and you make a mistake, your not logged.
I hope that helps,
maclaxguy
[ October 20, 2002: Message edited by: maclaxguy ]