I found this interesting as well. I have watched of the tutorials by Eleanor Burns on this subject. She demonstaits how to make the blocks and also gives a history for each block and tells how each message was protrayed in each quilt. It was very informative. Here is the link to her site and the underground railroad tutorials.
http://vimeo.com/30000326
This connects to part one, if you scroll down, you will see it listed videos, channel, group and album. I usually select the video one and I can watch all her videos from start to finish. Very interesting. Have fun and enjoy