Your Mac must have an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor to run Lion.

Mac OS X is the world?s most advanced operating system. Built on a rock-solid UNIX foundation and designed to be simple and intuitive, it?s what makes the Mac innovative, highly secure, compatible, and easy to use. Quite simply, there is nothing else like it.

http://www.apple.com/macosx/