The first step to learning Linux is actually installing it. I'll assume you're coming from Windows, mainly because I haven't used a Mac in about 8-9 years and things have changed with them since then. And if you're using something besides Windows, Mac or Linux, you probably don't need my help with anything!
There are some pre-requisites to installing it yourself, as there would be with installing any operating system: you need some computer know-how. You need to know things like what a hard-drive is. Same for drivers, although installing drivers is quite a different thing in Linux than in Windows.
You also need a desire to do it. Maybe it is curiosity about Linux itself, or maybe it is a desire to learn about it in order to do a job that uses Linux a lot like a network/systems admin.
The desire can't really be, "I'll learn Linux because it is the next big thing!" No, Linux is not the next big thing. I don't think you'll be able to make millions through Linux. Linux has this whole open-source thing going that sees ownership and property as damage, and routes its way around it. People have not been successful at selling Linux (at least not by selling it directly), and I highly doubt you will too.
One thing keeping many geeks away from Linux is the hassle of actually installing it. Usually you have to create a new partition (and therefore running the risk that something will mess up and you'll lose a ton of data - been there, done that), and then actually installing the system. Then if the install messes up after it's tweaked the master boot record, you're up shit creek without a paddle if you don't know what to do now.
You can do it this way. It's the way I did it when I first got into Linux. Fortunately I didn't have any problems getting it installed, and chances are you won't either. But there's still a risk.
There are easier and less risky ways to do it. Ubuntu has this thing called Wubi, which I think in theory is a great idea. I've never used it before since I was using Ubuntu before Wubi came out, so I don't know how well it works in practice. Feel free to tinker with it.
The way I think is good is through virtualization. This involves installing some software like VMware or VirtualBox which are programs that allow you to install other operating systems inside them, and they function kinda like a sandbox. You can interact with the system as though it were your system, but it can't access the rest of your system.
The benefit of this over Wubi is that you're not limited to Ubuntu (correct me if I'm wrong, but I think Wubi is only for Ubuntu unless you do some serious mucking). You download an ISO file (CD image) of whatever distribution you like, and install away. IMO the best newbie one is Ubuntu, but some other good ones are Fedora (a variant of the popular Red Hat Linux) and Mandriva (formerly Mandrake). I first used Linux with Mandrake several years ago, and then used Fedora when it came out - that was version 1, they're on version 10 now, wow! Another one I liked but isn't quite as newbie friendly is openSUSE (not sure how to pronounce that one, is it open-soo-see? open-soos?). Finally one that I've used that is very much not newbie friendly but a lot of people like is Gentoo, which is good if you want complete control and customizability of your system.