The definition of Linux:
From: http://en.wikipedia.org/wiki/Linux_kernel
>The Linux kernel is an operating system kernel used by a family of Unix-like[4] operating systems. The term Linux distribution is used to refer to the various operating systems that run on top of the Linux Kernel.<
The definition of a Linux Distribution:
From: http://en.wikipedia.org/wiki/Linux_distribution
>A Linux distribution (also called GNU/Linux distribution by some vendors and users) is a member of the family of Unix-like software distributions built on top of the Linux kernel. Such distributions (often called distros for short) consist of a large collection of software applications such as word processors, spreadsheets, media players and database applications. The operating system will consist of the Linux kernel and, usually, a set of libraries and utilities from the GNU project, with graphics support from the X Window System.<
After you've followed those two links and read the complete articles found there you'll be equipped to start researching different Distros to try from Live CD ( http://en.wikipedia.org/wiki/Live_CD ) before you settle on any one distro to actually install.
Informed suggestions of distros that are the most newbie/user friendly can be found here:
http://blogs.techrepublic.com.com/opensource/?p=382&tag=rbxccnbtr1
This is the quintessential place to start shopping for distros to try:
http://distrowatch.com
You can make your own Live CDs by burning ISO images of any particular Distro to CD. You'll need a CD/DVD burning ROM, an ISO 'burner' (program) such as Nero or simply ISORecorderV2RC1 (which I use on Win XP) and 'decent' quality data capable CDs to write to. ISORecorderV2RC1 is free and [if you need/want it] you can find it here:
http://aimini.net/view/?fid=FdpRuW60P4DFig8uQN34
I strongly suggest that you find a Linux User Group (LUG, for short) near you for person on person/computer help if and/or when you may need it. Here is where you can find a LUG near you to attend:
http://www.linux.org/groups/
That site also has a wealth of other Linux information contained within it, as well.
I hope this helps. Good Luck in your Migration to the Penguin!