I use MobieDRM Version 009 to crack my prc files. I have attacked the file below. All you need to do is get it here
http://paste2.org/p/646093, copying and saving into a 009.py file
Now you then put your .prc book into the same directory as created file.
Now just run the following
python 009.py in.prc out.mobi 'PID'
This version is the best working this far and can handle the newest mobi books.