The Nook is not like some other devices. You MUST use an SD.
The reason is you cannot flash ROMs with the stock recovery that comes with the Nook. You must use a custom CWM on SD.
Sent from my BN NookHD+ using xda premium
See my Nook Color Tips Thread here
and my Nook Color EMMC Partition Repair Thread here
and my Nook Color Updated CM SD Installation Instructions here
and my Nook HD/HD+ stock tips thread here
and my Nook HD/HD+ CWM Root Tools thread here