[Nook HD, HD+ General] HiddenG:
I'll attempt to describe this to you as easy as possible, and hopefully you should have your Nook ready in minutes. It doesn't take too much effort or time; mainly waiting for install requires time, other than that it's a quick process. It's not difficult either; the more you believe it is difficult, the more it will be. ;)

I'll start from the beginning; and you go can go from there. :)

1. Download the latest ROM for your Nook HD (this is a hummingbird variation) from: http://xdaforums.com/showthread.php?t=2063968

The latest version is, as of today (CTRL + F in your browser, then paste the first line of the following quote to find it easily):

2. Now you need to download the latest ClockWorkMod Recovery for your Nook (to install the ROM). Once you download it, you must also download the latest update file. Download CWM & the Update from: http://xdaforums.com/showthread.php?t=2097731

The latest version of CWM + the update, as of today:

Download both these from the link on step two (above; in this paragraph).

3. You optionally can install Gapps too; which I would recommend to access all of Google Services, including the Play Store. So download it from here: http://goo.im/gapps/gapps-jb-20121212-signed.zip

4. Let's get started! First, if you have a Windows machine, download WinDiskReader32 (click). This is to burn the CWM .img to your SD card. Now plug in your SD card into your PC. Extract the CWM files, it was downloaded in step 2. You should have a single file with the extension .img. Load up WinDiskImager, select the CWM file, and also select the drive which your SD card is inserted into. Make sure you do not overwrite any other drive (i.e. C drive), as you will wipe out your whole PC OS. Then hit the "Write" button on WinDiskImager. Your SD card will now have CWM installed (and your SD will be partitioned. This is fine, and you should only see around ~160MB on your SD card; again this is perfectly normal).

5. After burning CWM to your SD card, extract the update file (also downloaded in step two) directly into your SD card. So basically, extract the update file into your SD card, and it will ask if you want to overwrite any existing files, confirm this.

6. Connect your Nook to your PC, whilst on the stock B&N ROM and in MTP mode (if you don't know what MTP is, most likely you haven't changed it, so your can ignore it). Once plugged in. Transfer the ROM file you downloaded in step 1, and Gapps which you downloaded in step 3 to your Nook's "Internal Storage". Transfer the ROM & Gapps (DO NOT EXTRACT THESE FILES, JUST COPY THEM TO YOUR SD CARD) to your Nook HD's internal storage via PC. Once fully transferred, move onto the next step. :)

7. Turn your Nook off. Eject your SD card from your PC. Place the SD card into your Nook. Turn on your device. At this point, your Nook will constantly restart as it sets up your SD card (don't touch it at this point, let it do it's thing). After a while, you should be booted into CWM. This is when the process of setting up the SD card has been complete.

8. In CWM, select "install .zip from SD card", then select "install .zip from internal sd card". Locate and install the ROM. This may take some time. Once complete, locate and install the Gapps file.

9. This isn't mentioned in the original setup, or anywhere else, but I would recommend that you fix the permission of your Nook HD now, as a fresh install before you proceed to use it. Go to this thread: http://xdaforums.com/showthread.php?t=2233688 and start from Section 5 on the link, once done, return to this thread, then move onto the next step here.

10. Optionally (if you don't want to install, skip to step 11), now you can install a patch by leapinlar. For example, if you boot into CyanogenMod, you cannot use your internal storage. You can only use your SD card. However, if you would like to use your internal storage when in CyanogenMod, install this fix by leapinlar:

From: http://xdaforums.com/showthread.php?p=38153094#post38153094 If you install this fix, your internal storage will be used instead of your SD card (this is a bonus for those who are using 2GB SD cards, since they're limited on storage). After this fix, all your apps and everything will treat the internal storage as it's default native storage space.

11. Go to the root menu on ClockWorkMod Recovery, and select "reboot system now". Your tablet will now reboot into CyanogenMod perfectly.

You are good to go. All the best. :)