The best way to learn Linux is to use it. A good introductory book will help, but you won't really learn Linux or become confident in your skills unless you park yourself in front of a Linux system and start typing (and popping windows open, creating files, find your way around the desktop ...). And one of the easiest ways to start using Linux -- even before you've committed hardware to it -- is to run Linux in "live" mode. And one of the best ways to run in live mode is to build yourself a bootable USB drive using an excellent tool called UNetbootin.
To run Linux in live mode, you install a bootable release on a USB drive or DVD. Your hard drive is not impacted unless you decide that you like the Linux release that you're trying enough that you want to commit it to disk. This means that you can run Linux as much as you like without any risk of overwriting or affecting your currently installed operating system. The only down side to running Linux in live mode is that it won't save files that you create or changes that you make while you're logged in. Every time you boot from your USB drive, you return to the same original system.
UNetbootin (Universal Network Installer) is a superb little tool that makes it dead easy to create bootable USB drives from any in a large selection of available Linux distributions. These include Ubuntu, lubuntu (a small Ubuntu distribution), Debian, Fedora, SuSe ... UNetbootin runs on Windows platforms -- 2000, XP, Vista and 7 -- as well as Linux and Mac OS X (10.5 and later). You simply request the appropriate executable, selecting Windows, Linux or Mac OS from the buttons and download the UNetbootin version you need.
When you open UNetbootin, you can select from a menu of Linux distributions the one that you want to try. My 4 GB USB stick was far more than I needed, even for Fedora 17. The current release of UNetbootin provides easy access to 25 different Linux distributions each with anywhere from 1 to 6 different releases available.
UNetbootin can also be used to load a nice selection of utilities such as Parted Magic (a partition manager), SystemRescueCD (for system repair, backup and recovery) and Backtrack (for network analysis and penetration testing).
Check out http://unetbootin.sourceforge.net for downloads and more information on the Linux versions and utilities available.
Once you select the distribution and release that you want, UNetbootin will find the appropriate files and extact what you need, install the bootloader, and prepare your USB device for booting. The type should be "USB Drive" (the default setting) for setting up USB for live mode. The other choice is your hard drive. If already formatted as FAT32, your USB device should show up in the Drive: menu.
If your USB isn't formatted as a FAT32 drive, UNetbootin won't recognize it and will issue a message that says "No USB flash drives were found. If you have already inserted a USB drive, try reformatting it as FAT32." After reformatting the drive, you'll then need to exit UNetbootin and start it up again or it will continue insisting that it doesn't see any flash drives. If on exiting UNetbootin, a window pops up saying that the program might not have installed correctly, just click on "This program installed correctly" and you can get back to work.
Once you have selected your distribution and release, select "USB Drive" and the device you've inserted. For me, this was E:\. Then click OK.
Expect the building of your USB drive to take a while. Mine took just over an hour from clicking on OK to having a bootable USB device. Once your USB is ready, you will be prompted to reboot now or exit.
Before you can boot from your USB drive, your system needs to prioritize booting from the USB drive. This is generally done by holding down the F2 key while booting and then going into the setup to change the order in which the devices are selected. On some system, this might be F12 instead of F2. Your USB device should be first in your boot order list so that anytime you insert a USB stick into a USB port and turn on your system, it will boot from the flash drive rather than from your hard drive.
When you boot from the USB drive, you will be presented with a menu of boot options. These will include "default" along with an option to run in live mode and one to install on the hard drive. What happens when you use the default option will depend on the distribution and release that you selected. Choose the live mode if you're at all unsure how the default mode will run.
Booting from the USB drive should be pretty fast. It should take only a minute or so. Once your system has booted from the USB stick, your system should be up and running Linux. You can explore the desktop, gaze lovingly at all the nice options and tools in your start menu, open a terminal window and try out some Unix commands.
UNetbootin is not only useful for live mode, of course, but provides a painless way to install Linux on your hard drive -- one that doesn't require that you hunt down the distribution that you want to try or spend hours burning CDs or DVDs. UNetbootin prepares your installation media with very little effort on your part. All you need is a small USB drive (1G will probably do it) and an hour+.