1. read online, read here and asked here also asked at linuxnewbie.org forums.
linuxdocs.org, linuxnewbie.net (i think .net), google
2. Tried Mandrake 8.0, something went wrong and it all went to hell from the get-go. not to say mandrake is unreliable, tons of people use it w/ no problems. but in my situation for whatever reason it did not cooperate. then i installed redhat 7.1 and have been crash/freeze free. i am soon to move to debian, debian is more for the advanced linux user (i am not), but with some work you can figure it out, however for your first linux install it would not be a good idea. debian is probably the most "pure" linux, it is non-profit and only uses stable stuff (i.e. it is at kernel 2.2x whereas we are up to 2.4.9 now i think?), also the apt-get function makes isntalling apps a million times easier. wait till you deal w/ rpm's and dependencies, and source that wont compile, etc etc and you will see what i mean.
3. not sure of specific books, o'reilly books in general are good though, also a "for dummies" or "idiots guide to" type book would probably be a good start.
4. like it was said in the above post, unix is a general term, you cant really install "unix" on a system, unix is a blanket term which includes bsd, linux, hpux, solaris, and god knows what else (osx, which is bsd). bsd seems to be the most secure, there is openbsd, freebsd, and another one which i dont remember. wait till n0cmonkey shows up, he can tell you alot more than i can.
<< Or any OS for that matter. >>
well, win9x is not secure at all, and that is no stretch. there is no user based security, no file system permissions, nothing. winNT(2k and xp too) is alot more secure and is probably secure enough for any "normal person" but there are plenty of holes (>>IIS<<), look at nimda and code red for example. like i said, winnt is secure enough for most people, but it's not perfect (nor is anything, but you get the point)
good luck