You've heard about all the benefits of using Linux: it's fast, stable, secure, and it really is easy to use. If you're ready to give Linux a try on your own computer, you have several options. Some require less commitment than others.
For example, you might want to try running Linux from a "live CD." This option loads the operating system into RAM, and doesn't write files to the hard drive, which is one of the main benefits of using a live CD: it makes no permanent changes to your computer, and uninstalling it is as simple as removing the CD.
Another advantage for live CD distributions is that you can use them almost anywhere. Take the CD or DVD with you and pop it into just about any computer, and you'll have Linux at your fingertips without having to install anything.
Using a live CD has its drawbacks, too. It runs slower because the operating system is running from the CD instead of the hard drive. Since CD-ROM/DVD drives are much slower than hard drives, running off a live CD won't give you the same sort of speed that a hard drive install will.
Another problem is that any changes you make, such as custom configurations, will disappear every time you shut down the live CD. Some live CDs compensate for this by allowing you to write data and configurations to the hard drive or a USB drive, but it requires some special setup.
Despite these drawbacks, a live CD is probably the best way to test drive Linux. There's no risk in using the live CD, if you don't like it, just pop the CD out and go back to what you were using before. If you like the OS, though, you may want to go further and put Linux on your hard drive.
Installing on a partition
Installing Linux on a partition of your hard drive is easier than ever. All you have to do is put the Linux CD in your drive and follow the instructions. The vast majority of Linux distributions will recognize that you have Windows installed and will help you set up a new partition just for Linux, using some or all of the free space on your drive. This is called dual-booting.
When you reboot your computer, instead of booting straight into Windows, the computer will display a menu for you to select your operating system. If you make no selection, the computer will boot into the default operating system, usually Linux, so if you want to boot into Windows, you'll either have to pay attention, or change the default settings.
Removing Microsoft Windows
If you want to try Linux out all by itself, you can tell Linux to take over the hard drive and use all the space for itself. Once this operation is completed, you cannot change your mind and get Windows back unless you have a restore disk, and even that will only restore the factory default settings.
We're all about Linux here, of course, but we do recommend that you make a full backup of your data before taking this route in case you decide you need to revist Windows at a later date -- or just need access to your data. Many people have removed Windows from their computers and report great success in using only Linux for their day-to-day activities.
Buying Linux pre-installed
If you're not averse to spending some money, and you'd rather skip the "do-it-yourself" routine, you can buy a computer with Linux pre-installed. The biggest advantage of doing it this way is that you know the computer is configured correctly and that Linux will work the way it is supposed to. Your computer is under warranty, and most companies provide technical support for a certain period after purchase.
If you need help
One of the nice things about using open source software is that there is no shortage of help available, should you need it. The first place to go is online. Search to see if your question has already been answered somewhere. You might find the answer in a discussion forum, or in a Linux HOWTO.
If you have searched diligently and haven't been able to solve your problem, then trying asking a question in one of the discussion forums. You have a better chance of receiving useful answers if you document your question fully, including a description of the hardware you are using, the distribution, the exact nature of the problem/question, any error messages you received, and the steps leading up to the error.
Most IRC networks have Linux help channels if you would like to try some realtime assistance. The same etiquette rules apply, and don't expect immediate answers.
If it is hands-on help you need, consider visiting a meeting of your local Linux Users Group (LUG). Many LUGs set aside time at each meeting specifically to answer questions or help install Linux. LUGs also usually have a mailing list, so you can ask your question before the meeting.