Its been mentioned on a few forums now but can't see it here so worth adding.
There is a programme around that allows a lot of Canon DIGIC-II and -III compact cameras to shoot in RAW mode and provide many more options such as live histogram, "zebra" mode, DOF calculator and so on.
The programme simply auto boots off the SD card and doesn't upgrade/alter the existing firmware in any way at all. It works on a lot of the Powershot range, Ixus range, G and S ranges and so on.
I've installed it here on my A620 and it's working perfectly in RAW mode along with the other above mentioned features so is worth a try.
The software is free and open source.
Anyone interested the program is here:
CHDK - CHDK Wiki