The reason Apple ships a one-button mouse is to *enforce* the idea that anything you can do in any app should be doable with only one button, and doable with the mouse. This results in apps that are easy to navigate, easy to find functionality in, and just plain easier to use. Developers can't rely on that second button being there, so they have to make everything doable with a single button. Ie, left-click.
Windows apps are, generally, harder to find things in because a *lot* of things are hidden under *only* right-click... in MacOS X apps, the contextual menu from right-click is completely redundant, but just a shortcut for often-used items.
Bottom line: if you want a two (or three, or five (yes, they exist)) button mouse, you'll have to buy one. It's strictly for convenience.