Mac OS X 10.6 requires a Mac with an Intel processor.
Upgrading from Mac OS X v10.5 Leopard:
If your Mac is running Mac OS X v10.5 Leopard, just purchase Mac OS X v10.6 Snow Leopard and follow the simple installation instructions.
Upgrading from Mac OS X v10.4 Tiger:
If your Mac is running Mac OS X v10.4 Tiger, purchase the Mac Box Set (part number 7876357 or 7876358), which is a single, affordable package that includes Mac OS X v10.6 Snow Leopard; iLife ’09, with the latest versions of iPhoto, iMovie, GarageBand, iWeb, and iDVD; and iWork ’09, Apple’s productivity suite for home and office including Pages, Numbers, and Keynote.