I've been messing around with that same tutorial and hit the same wall. if you were going the same as me I'm assumung you added the folder to your user directory and not the install directory?
Put this into the boards.txt file in the install dir (Program files in my case)
##############################################################
atmega328bb.name=ATmega328 on a breadboard (8 MHz internal clock)
atmega328bb.upload.protocol=stk500
atmega328bb.upload.maximum_size=30720
atmega328bb.upload.speed=57600
atmega328bb.bootloader.low_fuses=0xE2
atmega328bb.bootloader.high_fuses=0xDA
atmega328bb.bootloader.extended_fuses=0x05
atmega328bb.bootloader.path=atmega
atmega328bb.bootloader.file=ATmegaBOOT_168_atmega328_pro_8MHz.hex
atmega328bb.bootloader.unlock_bits=0x3F
atmega328bb.bootloader.lock_bits=0x0F
atmega328bb.build.mcu=atmega328p
atmega328bb.build.f_cpu=8000000L
atmega328bb.build.core=arduino
atmega328bb.build.variant=standard
With this I managed to get it building the Blink example. It seems to look for the additional files it needs in the same folder as the boards.txt file - you could keep it out in another dir, but you would need to copy the cores and possibly bootloaders directories.
Hope it works for you 