Linux is an operating system, like Windows or OSX. The main difference between Linux and Windows/OSX is that Linux is Open Source, or that anyone can look at it's code, and make changes if they want to/read the developer comments
1. Linux is free (as in speech).
2. Linux is (usually) free (as in beer).
3. The community support for Linux is excellent.
4. Linux is VERY stable.
5. Linux is immune from 99.9999999999999% of viruses. (Last time I checked, there were 4. And all required you to do something very complicated and intentional to install.)
6. Linux is very customizable.
7. There are many different modern distributions of Linux. (Instead of there being only one current version, as with Windows).
8. Most Linux distributions are designed to be usable out of the box (office suite, photo editing software, media players, email clients, web browsers, etc).
9. Linux has a thing called repositories, and you can use a program called Synaptic to install pretty much anything you want off of the internet (instead of having to browse the internet, download the files, install the files, update, etc.)
10. Linux has a centralized updating system, meaning that you use one program to update ALL of your software.
11. Linux can run on very fast computers, and very slow computers. (I got it working on a 386.)
12. Linux has a program called WINE that lets you run some Windows programs. There are also different programs (like Cedega) that are specifically for games.
13. Linux is scientifically proven to up your cool factor.
1. Most commercial software was not written for Linux, so it will not work unless you use an emulator.
2. Driver support for proprietary products isn't that good (but it's getting better).
3. Commercial support costs moneys. Lots and lots of moneys.
4. You usually can't buy computers with Linux preinstalled. (Dell has some for sale, and a lot of micro-laptops are also coming out with Linux on them.)
5. Linux requires you to use the terminal some. It's not that hard though.
6. Linux has a UNIX-like filesystem (like OSX) that starts with root (/), and everything bases from there, instead of using drive letters (C:). This is confusing for some newbies. You get used to it after a bit though.
The main requirements vary with Linux, from stripped down text versions that run on almost nothing, to uber-shiny fancy ones that will make your computer blow up if it isn't brand spanking new.
All Linux distributions look different. Some look like Windows. Some look like DOS. Some make you think "WTH were the programmers smoking when they designed this". And some look like something of their own. It's extremely diverse.
The one I use is Ubuntu
. It's easy to use and looks nice.
A dual boot is pretty easy. You just have to tell the installer to shrink the Windows partition (or, if you're feeling cocky, you can manually partition it out), and the installer does the rest.