I am pasting this from a PM from earlier, hopefully it can help you out.
If you are rooted its pretty easy.
[ZIP][DEV][ROM] Nookie Froyo 0.6.8 (02/15) CWM flashable! - xda-developers
Download the Nookie Froyo Flashable ZIP file, NOT the SD card one, the one that says CWM flashable, dont extract it, just place it to the root of your SD card, not in any folders. Then place the SD card into the nook, note this shouldnt be a SD card that has a bootable ROM on it, use a different one, or format the one you have and use it for storage only.
Go to ROM Manger and hit reboot into recovery.
When the phone boots into Recovery menu, use the volume keys to scroll through, make a backup if your internal memory needs to be, that way you can revert it back if you dont like Froyo.
After the backup, hit power to go to the main menu if its not there already, go to Wipe Data/Factory reset and confirm the action.
Then go to Install ZIP from wizard, then Choose ZIP from SDcard, then scroll to the Nookie Froyo ZIP you put on there, and select it, and confirm. It will take a minute to finish, then reboot the phone, it will now boot into Froyo.
For GApps like Market and Gmail, etc, it really is a pain so to tackle that, you'll need a lot of patience. You'll need adb first, go here:
[DRIVER PACK] Easy USB ADB Installer for Windows (32/64 bit) - xda-developers
that will install adb for you, or it should.
The Nookie Froyo thread has a link to a WIKI at the very bottom, then go to Next Steps and click that link, this page will show you how to Install the GApps through adb.
It took me the majority of a day to figure all this out, and its not nearly my first time modding things, so expect a lot of hurdles, but once its done, its great.
There is an easier way to get GApps on there, if you can find a flashable ZIP file containing GApps, which I couldnt find/couldnt get to work, and had to do the hard way.