If you are thinking of Lion then the supported hardware is all Intel based processors
To use Lion, make sure your computer has the following:
An Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor
Mac OS X v10.6.6 or later to install via the Mac App Store (v10.6.8 recommended); you can install without Mac OS X v10.6 by using an OS X Lion USB Thumb Drive, available on the Apple Online Store
7 GB of available disk space
2 GB of RAM
If your Mac does not meet these requirements, you will need to upgrade your Mac before installing Lion.
If you are looking to move to Mountain Lion these are the supported Hardware
iMac (Mid 2007 or newer)
MacBook (Late 2008 Aluminium, or Early 2009 or newer)
MacBook Pro (Mid/Late 2007 or newer)
Xserve (Early 2009)
MacBook Air (Late 2008 or newer)
Mac mini (Early 2009 or newer)
Mac Pro (Early 2008 or newer)