Early K10D firmware hack attempt
I took some information from this abandoned project.
Firmware hack thread by Rule 34 on DPReview forums
Contains some extra information, but not much. Most information on links in this thread is not available anymore.
Debug mode program
You could use DLL inside this program to control many parameters of camera and, possibly, dump firmware.
Software for tethered shooting using Pentax DSLRs, providing the functions from Pentax Remote Assistant to Linux users.
(c) 2009 Pentax Hacking Community