catsknit,
Here is a step-by-step from the beginning. The steps are supposed to be the same as my HD+, but I don't have an HD to test it on. All information was taken from the XDA developers web site and they deserve full credit, not me. I'm just trying to explain it a little better. All links were working at the time I posted this.
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The following files are for the Nook HD only!
Download the latest CM10.1 ROM:
cm-10.1-20130104-UNOFFICIAL-hummingbird.zip
Download the latest Google Apps:
http://goo.im/gapps/gapps-jb-20121212-signed.zip
You will also need updated cwm image:
sdcard-cwm-hummingbirdv3.img.gz
For first time install only (you will need 4G or bigger SD card, smaller ones are not supported and not tested):
Unzip cwm image and write it to your SD card (entire SD card not just one partition of it), use
Win32 Image Writer if you are using Windows. If you’re using Mac, you’re on your own. Make sure to use
SD card rated for fast small IO for best results.
Your Nook should be powered off.
Insert the card into the Nook and turn on the nook, CWM should start. The image your wrote onto your SD card in the first step will automatically repartition the card into a correct layout no matter the size (but no smaller than 4G).
CWM (Clockwork Mod) is like using the BIOS settings on your desktop computer. Use the volume keys to scroll through the options, the N button to select, and the power button to go back to the previous menu.
In the CWM:
Go to "mounts and storage", choose "mount /sdcard".
Press power button to go back to the main menu.
Just turn off the nook at this stage and remove the SD card. You will need to copy the zip files to your SD card. Your SD card is now formatted with four partitions (“drives”) on it. Windows will only let you access the first partition (“Boot”), so you need to use Linux.
Download the latest version of Ubuntu from here:
http://www.ubuntu.com/download/desktop
Just get the 32-bit version regardless whether your Windows is 32 or 64 bit. Click the button that (currently) says “Get Ubuntu 12.10”. You don’t have to donate, you can scroll to the bottom and click the “Not now—take me to the download.”
Ubuntu will download as an ISO file. You will need a blank DVD. Use whatever DVD burning software you have installed on your computer, or in Windows you can right-click on the file and choose “Open with” and then “Windows Disc Image Burner”.
Once that’s done, reboot your computer with the Ubuntu disc in your drive and make sure it boots from your DVD drive (you might have to press F12 or change some BIOS settings). It will eventually come to a window with a choice to either Try Ubuntu or Install Ubuntu. Obviously, you want to try it.
Put your SD card into your computer’s card reader and copy the two zip files (cm-10.1-20130104-UNOFFICIAL-hummingbird.zip and gapps-jb-20121212-signed.zip) to the volume named "CM10SDCARD" (not "boot"), then put the SD card back into your Nook and power it on again. Copy them just as they are—do not unzip them.
Your Nook should come up in CWM and you will need to choose "install zip from sdcard", and then "Choose zip from sdcard" and then select the “cm-10.1-20130104-UNOFFICIAL-hummingbird.zip”. When that one finishes, do the same thing with “gapps-jb-20121212-signed.zip”.
When they are both done installing, press the power button to go one level up in the menu and then choose reboot. This will reboot you into CM10.
If you ever need to get back to CWM later, use either "reboot to recovery" power menu, or reboot, and once B&N nook logo shows up, press and hold power and home keys together for about 4 seconds.
To reboot into stock nook software, just power off, remove SD card, then power on.