Yesterday, we reported how the new Kindle Fire was going to be harder to hack this time around. As it turns out, the Kindle Fire 7 HD has already been rooted. The method is not exactly new. It is based on the one that was found on the Transformer Prime running ICS. In fact, it should work for other ICS-running devices as well.
Android P0lice already has the instructions you need to root your Kindle Fire 7. It is going to take hackers a bit of time to install other versions of Android on the Kindle Fire though. But this is a good start. You could always get some help on Rootz Wiki if you get stuck.