CNET wrote a post recently on turning a Nook Color or Nook Tablet to a full Android tablet running Jelly Bean. Their option was to purchase an N2A Card image for $19.99 which will be burnt to a microSD card. A card with N2A preinstalled can also be bought starting at $30. The microSD card would then turn to a bootable image of Jelly Bean. The writer confirms that everything worked fine using this setup.
But actually, you don’t have to pay to get Android Jelly Bean for your Nook tablet. All you need is Cyanogen Mod 10 or CM10 from the good guys at XDA developers. This link should get you there. The thread starter is modest enough to say that this project is far from perfect. The good thing is that a lot of people have been using this mod which means any problem that’s found could have been solved already.
This mod could turn make your Nook tablet similar to Nexus 7, at least in UI. If you don’t want to spend time configuring then you could go for the N2A option.