Here's a guide that outlines some basic and interesting things about Mac OSX that will make any Windows user completely at ease if you ever end up having to work on Macs. Here's an excerpt:

The first thing you should notice even before powering on your new Mac is the keyboard and mouse. There isn't a Windows key anymore, and the Alt button now has the word "Option" on it. The Windows key has been replaced by what is commonly called the Apple or Command key, and for the large majority of hotkeys, will replace the Ctrl commands normally found on Windows.

You should also happily take note of three keys: F9, F10 and F11. These three keys make up Exposé, which is currently a Mac-unique feature that makes working on a computer infinitely easier. F9 miniaturizes all of your open windows and lets you view all of them. F10 miniaturizes your open windows in the program you're running, and F11 pushes all windows out of the way to expose your desktop. See Expose section later.

The mouse might seem peculiar to you; it's only got one button! This serves as the left-click on Windows systems. What if you want to right-click? You have two options here: you can either Ctrl+click or hold down the click to bring up the oft-expected Windows-right-click menu.

After you've gone through initial set-up of your Mac, you'll be left looking at your desktop. Take note of a few things: Your taskbar, originally at the bottom of the screen in Windows XP, is now at the top. From left to right, you'll see an Apple, Finder, some menu options (File, Edit, etc.), and on the far right, what amounts to your tray (the icons that were next to your clock in Windows), the time, and a little magnifying glass known as Spotlight. Finder is the equivalent of Explorer on Windows.

Another similar article can be found on ExtremeTech. That one covers both Windows users trying out OS X, and Mac users trying out Windows.