I've used Linux off and on for about ten years now. It's a LOT more user friendly now than it was when I started out with it back in high school. For someone just switching over from Windows I would recommend Kubuntu. It's an off shoot of Ubuntu, just a different user interface mainly. The part that is most confusing for new users is what Nate was asking about -- the different distributions. They all use the same base, which is Linux itself, but package different programs and interfaces with them. Some are source code based distributions, which means they come with just the source code and you compile the entire operating system yourself on your machine when you install it. Others use specific interfaces, such as KDE or Gnome, which handle the way your desktop looks and acts. The greatest thing about linux, which is the enormous amount of choices for how YOU want to do things, is also the greatest downfall of it when it comes to new users.

As far as pros and cons? Linux is free. 90% of the programs for it are also free, and you can download them at will, legally. Most anything you can do in Windows you can do in Linux. The only downfall that I see, and this is the reason I'm running XP right now, is the lack of up to date games. If you don't do much PC gaming, then obviously this is a moot point for you.

Also, if you decide you'd rather stick to Windows, I'd recommend holding off another year if you can and wait for Windows 7 to be released. Don't bother with Vista.