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Looks like Snow Leopard does not boot into a 64bit kernel by default. There are a couple of ways to get some 64bit goodness.

Boot Keyboard Shortcut

Hold down the ’6′ and ’4′ keys while you are booting. Conversly, you can boot into 32bit by holding down the ’3′ and the ’2′ keys.

NVRAM setting

Set a nvram setting to boot into 64bit.

nvram boot-args="arch=x86_64"

Apple Configuration File

Set to Apple configuration file to boot into 64bit by editing /Library/Preferences/SystemConfiguration/com.apple.Boot.plist

< ?xml version="1.0" encoding="UTF-8"?>
<  !DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
< plist version="1.0">
< dict>
	< key>Kernel< /key>
	< string>mach_kernel< /string>
	< key>Kernel Flags< /key>
	< string>arch=x86_64< /string>
< /dict>
< /plist>