Want to leap into Linux? Try Ubuntu
I have been using Ubuntu now as my main operating system for a few years and if there is one Linux distribution to suggest, Ubuntu is the one. Have access to thousands of applications, setup a LAMP server with just a few clicks... oh did I mention it's free? (of course). Their forums are also a great place to get help or learn more.
Oddly enough, Dell has just picked them up as well. Should do a nice job of getting their name out there!
But, is it going to make me go out and buy a Dell? Nah, Dell hardware isn't that great.
Visit Ubuntu's official site.