Canon only supplies drivers for my G3 that are compatible with Windows XP. They don't work in Vista or Windows 7. Until today, in order to download pictures from the camera I've had to either keep an XP installation on my PC, use Ubuntu Linux or an external flash card reader.
I found a post on the Microsoft TechNet forums (Canon EOS 20D compatibility
) about similar troubles with a Canon EOS 20 camera with a work-around that works for me too. It might work for other Canon cameras also.
Just change the "Communications" setting from "Normal" to "PTP". Now Windows 7 recognizes the camera and I can transfer files.
It's a bit slow, like USB 1.1 speeds, but it works!