It looks like not all users understand about 64-bit support in snow leopard.
So, here is how it works:
on all Macs, except xserve, system boots by default 32-bit kernel.
This kernel can run 64-bit apps justs fine on core 2/core i7 based cpuz.
64-bit kernel works only on macs with 64-bit efi, this is limitation set by Apple,
technicaly 64-bit kernel can be launched by 32-bit efi just fine.
also Apple disabled 64-bit kernel support for any macbooks, even with 64-bit efi.
64-bit Kernel can run both 32 and 64 bit apps.
On hackintosh only cpus with ssse3 can run 64-bit kernel/apps, its core2/corei7 based cpus.
if kernel is 64-bit, then it can load only 64-bit kexts.
if kernel is 32-bit, then it can load only 32-bit kexts.
Userspace program cant load plugins with other architecture, for example menumeters will work only when you booted legacy, so menubar created by 32-bit application.
Quicktime uses InterProcess Communications(IPC) to load 32-bit codecs in 64-bit player.
64-bit safari uses IPC to load 32-bit flash player plugin.
To try to boot x86_64 kernel on Macintosh, edit this file:
and change it to