Prince McLean, AppleInsider

Build notes leaked on the web of a prerelease version of Mac OS X 10.6 Snow Leopard indicate that the software only supports enabling its new 64-bit kernel on certain machines, including the Xserve, Mac Pro, and MacBook Pro, but this does not mean Snow Leopard’s kernel will be limited to 32-bit operation on consumer machines.

Road to Mac OS X Snow Leopard: 64-bit to the Kernel