This one is actually the easy part.
One way to get Linux is to buy a copy. Head down to your local computer software store and ask for your favorite distribution. Alternatively, visit your favorite vendor's Web site, whether it be Mandrake, SuSE, Red Hat, or any of the many different distributions listed on the DistroWatch (http://www.distrowatch.com) Web site and order one online. Incidentally, DistroWatch also lists the top 10 major distributions at any given time.
Which distribution should you get? Well, every Linux vendor does things a little differently. If you think of this in terms of cars, it starts to make sense. Every single car out there is basically an engine on wheels with seats and some kind of steering mechanism so that drivers can get to where they want to go. What kind of car you buy depends on what else you expect from a car, whether that is comfort, style, the vendor's reputation, or any great number of other choices.
You really want me to suggest something? Let me start by saying that I think it is a wonderful thing that so many Linux distributions exist. Aside from creating a rich OS landscape, it furthers creativity and fosters innovation in software design. This can only be a good thing. However, if you push me for a suggestion and you are just getting started with Linux, I would probably suggest Mandrake first. It's an excellent, well-engineered, and beginner-friendly Linux.
You might be asking the question, If I can get a free copy of Linux, why would I want to pay for one? As it turns out, there is more than one answer to that question. The first is that buying a boxed set usually gets you some amount of technical support from the vendor. If you are feeling nervous about your first Linux installation, this might be a good reason. Second, the boxed set usually contains some kind of manual or manuals specific to that version of Linux. That will inevitably lead to another question as to what makes this Linux different from that one. Finally, in purchasing a boxed set, you are supporting the company that put leather on the seats or tinted the windows. It's a way of saying, "Thanks for all the hard work."
Because it is possible to get a free copy of Linux, you don't have to shell out the dollars if you don't want to. At most, you'll need a fast Internet connection, a CD burner, and some blank CDs?or a helpful friend who has these.