Poke around on the Yahoo group "cheapdigitalcamera" (http://groups.yahoo.com/group/cheapdigitalcameras/) if you just want to get your cameras patched and working. If you are looking for a challenge, head over to the CameraHacking forum (http://camerahacks.10.forumer.com/)
The first site has a lot of tools you can download to help you get your camera patched (in some cases, in as quickly as 5 minutes). Some of the tools are a bit out of date, but the libusb and pv2resurrector on the site are good. I would suggest downloading the latest pv2tool (2.13) directly from the sourceforge site, instead of using the copy on the cheapdigitalcameras site. (it changes frequently). Note that if you use any of the firmware or flash images, you can be considered "tainted" should a copyright issue arise from your future efforts.
The second site has a technique which can be used to extract your unique key (challenge/response key) without changing the firmware at all - and allows you to remain "clean", if you are planning on helping out with the hacking efforts in the future. Keep in mind, if you become a regular on that site, they don't like using rogue firmware because of the copyright issues.
I personally suggest attempting the SDRAM scan method (the "legal" method) first - because if it works, you are done, and you don't have to worry about having trashed something important we don't know about yet. (we are still debating about the calibration file).