Linux
Congratulations! You are about to embark on a journey of enlightenment!
There is a huge, and I mean huge, amount of info on Linux on the Internet. Looking in Google's directory, under Computer/Software/Operating Systems/Linux reveals over 3,000 links. A Google search for "Linux" resulted in over 48 million hits.
For starters, go here:
www.linuxnewbie.org
This site also lists other links.
There are several Linux distributions. I personally use and recommend Redhat Linux. There website is also packed with info:
www.redhat.com
For newbie books, I like How To Use Linux - Visually in Full Color, and Teach Yourself Linux in 24 Hours both by Bill Ball and published by Sams Publishing.
A couple more books you will want are Running Linux, 3rd Ed. by Matt Welsh, and Linux in a Nutshell by Jessica Hekman, both from O'Reilly Press. These are not newbie books and will be rather intimidating at first, but they are valuable references.
You might also want to go to my local (San Diego area) Linux user group website and sign up for their "Newbie" e-mail list. Here you will find a group of dedicated Linux pros who love helping newbies get started. And no, you don't have to live in San Diego. :-)
www.kernel-panic.org
You will probably want to invest in software such as "Partition Magic." This will allow you to create a Linux partition on your hard drive while preserving your existing Windows system. You will then have a "dual-boot" system - you will be able to select Windows or Linux when you boot up your computer.
The Redhat personal edition comes with two books which are also essential reading before you attempt your install.
As Morpheus said in The Matrix, "Welcome to the Real World."