UPDATE 05/28/13 - Now that verygreen has changed his SD scheme to his new version, this guide should not be used on his ROMs dated 5/27 or newer. Use his new image and follow his new instructions. If you want to see the old instructions click on the Show Content button below.
Setting up the SD
Begin by downloading the files you need either with stock or your PC. You will need my updated SD image file, attached below (do not use the early4 image from the verygreen thread), the CM ROM zip you want to install and the gapps zip to match it. Put the last two zips on your internal media sdcard built into the HD+. You can get the HD+ CM10 ROMs here and the HD+ CM10.1 ROMs here. You can get the gapps zips here, 20121011 for CM10 and 20130301 for CM10.1.
Extract the SD image zip and you will have a 117MB .img file. Burn that to your SD with Win32DiskImager in Windows or the dd command in Linux or OSX. The SD needs to be at least 4GB and preferably a SanDisk Class 4.
To use Win32DiskImager, find it on the web (here, it's free) and install it on your Windows PC. Open it (be sure to run it as administrator) and select the drive (device) that has your card reader with your SD inserted. Then in the image file box put the location where you have the extracted img file. Then when everything is set right, click on the write button. A warning will pop up asking if you want to proceed. When you have verified that you are going to write to the correct device, click on Yes. (One user overwrote their external USB hard drive by not verifying first.) If you get an error message about access denied, it means you are looking at the drive with Windows Explorer. Close Windows Explorer and try again. In fact, it is a good idea to close all unnecessary windows when burning, even your browser.
When burning is complete, insert the SD into the Nook and boot. It should boot to the cyanoboot logo and sit there for a little while while it creates the other partitions on the SD and formats CM10SDCARD. Then it will end up in CWM for HD+ Original SD. If it does not leave the cyanoboot logo within a reasonable time (it hangs sometimes), just touch the power key and CWM should come up. To use CWM, press the volume up/down keys to move the cursor and the n key to select an item. The power key is the back button.
You can use the "install zip from SD/choose zip from internal memory" option to flash the CM ROM you downloaded earlier to your internal memory sdcard. Then you can flash the right version of gapps to match your ROM.
When you reboot (you need to leave the SD in the slot), the CM ROM should start. You will need to register with Google to set up Play Store.
If you later want to upgrade your ROM to another build, download it to your CM10SDCARD partition using CM. Then boot to CWM and flash it.
This version of CWM lets you back up and restore your setup. You can even back up to internal memory. It does not back up /boot, but does back up /system, /data and /cache.
Swapping EMMC and SDCARD
Some users have installed CM to a small SD card and want their apps to use the large internal media storage to store their data. I have developed a couple of zips to swap EMMC and SDCARD when booted to CM so that internal memory is available to your apps to store their files. One zip will add the swap and one will remove it. Get them attached below.
These zips can be flashed with CWM but will only install to the Original SD with CM. I just fixed a bug in the rev0 and rev1 zips. If you already flashed rev0 or rev1, you need to flash the remove zip before you flash the rev2 fixed version. No need to boot in between.
With rev2, both SDCARD and EMMC will show internal media storage, as will both MTP folders. A new folder, ext_sdcard, will show the external SD media partition.
Updating earlier versions of CWM
Updating prior installs of the Original SD installation to this new version of CWM is easy. Just download the ramdisk zip file attached below and extract the file. Put your old SD setup in your PC and rename the ramdisk.cwm to ramdisk.cwm.bak. Then copy the new ramdisk.cwm you just extracted to the card, replacing the version that was there. Next time you boot to CWM, the 188.8.131.52 version for HD+ Original SD will be there.