If you get a copy of the 2008 TurboTax demo CD for the Mac, you'll find that when you insert it on a Mac running Leopard, it doesn't work. But don't give up, even though it won't run automatically, you can still get it to run. Just insert the CD and navigate to it in the Finder. You'll see a file called Turbotax.app. Right-click on it and choose the "View Package Contents" option. You'll see that there are two DMG files, one for the premier version of TurboTax, and one for the deluxe version. Open either of the DMG files and TurboTax will install and update itself to work on Leopard (assuming you have an internet connection).