http://howto.wired.com/wiki/Supercha..._CHDK_Firmware
This article provides instructions on how to hack the firmware of your camera (they covered the Cannon series camera's in the article.
what the patch does is unlock features already in the firmware, so the process is reversable.
pics possible with this mod:On a standard Canon, for example, the fastest shutter speed option offered is 1/1,600 second, but the hardware can handle much more than that -- up to 1/60,000 of a second.
CHDK, the Canon Hacker's Development Kit, is an open-source software project that can be loaded on cameras using Canon's DIGIC II or DIGIC III firmware platforms. It unleashes new features including RAW file format, live histogram display, a battery readout, and the ability to run scripted actions on a camera.
pretty cool stuff.. 8)
here is the blog link
http://chdk.wikia.com/wiki/FAQ#Q._Wh...HDK_program.3F