
AC has the instructions: "All you have to do to get the custom recovery files to boot is copy the files provided to a card, insert it into the tablet and reboot. (You don't even have to format the card, unlike some Nook Color methods.) Once inside ClockworkMod Recovery, you can flash custom software or use another hack to get ADB file pushing from your computer. Flash the root ZIP file and you're done."
For now the root method works on Nook Tablets with firmware 1.4.1 or older.
Get the files and more detailed instructions here (via XDA user "Indirect"): http://forum.xda-developers.com/showpost.php?p=21895025&postcount=14