Download and try the following OS, and give it a go.

OpenBSD v4.7

OpenBSD is a multi-platform 4.4BSD-based UNIX-like operating system, and is fast, simple to install and secure “out of the box”.

1. Download installation files
2. Read the Installation guide
3. Read the Frequently Asked Questions

A good introductory book for OpenBSD is the “OpenBSD Command Line Companion” by Jacek Artymiak. It walks you through an install and an intro to OpenBSD.

Other books on the OS are:

• Absolute OpenBSD: UNIX for the Practical Paranoid
• The Book of PF: A No-Nonsense Guide to the OpenBSD Firewall