Mike499... First, thanks for your purchase again this year. All your previous years' tax return are just fine. They are completely compatible with the TurboTax software prior to 2012. Whether you download the 2012 TurboTax software or use the CD, you'll still need Mac OS 10.6.8 or higher and 64 bit processor. Download or CD doesn't change that.
With that said, I would encourage you to use TurboTax Online where you'll be able to prepare your 2012 return AND transfer all prior year information forward. Nothing is lost and in fact, everything is preserved. Furthermore, TurboTax Online allows you to save your data file to your computer when you're done so if you subsequently get a new Mac, you can switch back to the "desktop" version without losing any historical data. Plus, the system requirements for Online are significantly less. I'm sure you won't have any issues there.
If this is something you wish to pursue, please drop me an email at "turbotax_advocate" + "@intuit.com" (put these together for my valid email) so I can ensure you won't pay any additional money to switch to Online.
Thanks for raising a great question.
Bob Meighan
VP, TurboTax