http://liliputing.com/2011/12/early-buggy-build-of-android-4-0-for-kindle-fire-now-available.html
This is an early build of Android 4.0 Ice Cream Sandwich for the Kindle Fire. It's still very buggy. You can find out and how to install it at:
http://liliputing.com/2011/12/how-to-install-configure-android-4-0-on-the-kindle-fire.html
Update: The sdcard is now supported:
http://forum.xda-developers.com/showthread.php?t=1411895
