If you are looking to add Google Play and non Nook Apps to the HD, probably the easiest way to do it is to follow the instructions in the original post of this thread
. The post is updated on a regular basis, and links to the files that you need are there.
I'd suggest reading it a couple of times first, there is a lot of information, but it is actually very straightforward. I did this a few days ago, and it took me about an hour, total (after I had read it).
You will need a blank SD card, and an SD card reader on your computer. He has step-by-step instructions, but essentially it is (for Windows):
download and extract a file to your computer (clockworkmod). Burn that image to your SD card using a specific program that is freeware. Copy over one or more of the zip files (do NOT unzip them) to the SD card, using windows explorer. Then put the SD card in the Nook and reboot, and follow the installation instructions in the post. (I also did a back-up of the Nook before I installed, using the clockworkmod interface on that SD card, which was easy enough to do.
He has several different options. I just installed the Gapps/Play Store plus extras zip.
Note, you do NOT need to root the Nook to get the google play store on, or to install apps directly from the stores. I didn't root mine, and I've put on the google play store, Amazon App store and another one and downloaded and installed apps from each. He does have a zip which allows you to painlessly root if that is what you desire.
If you have any specific questions about the process I'm happy to answer them if I can based on my experience.