How do you know if your Snow Leopard upgrade is booting in 64 bit? Try these commands
ioreg -l -p IODeviceTree | grep firmware-abi
This command will check if your EFI is 32 bit or 64 bit the EFI can make or break for your 64 bit hardware running in 32 bit. There is a list of not too old Macs not being able to run in 64 bits because they have a dated version of the EFI.
To check if you are running the 64 bit Kernel, Type
in terminal and if your response contains the string x86_64 in the output that means you are in luck.