EDIT: I actually have it working, though I need to turn on the card via the PLAY button, and load it via firmware update in the MENU. I also have to lock the card before CHDK works.
I'm trying it out without partitioning the card to contain a FAT16 partition. I don't want to use it full time yet, as I'm testing it. My G10's firmware has been updated to 1.0.2.0.
It appears to load when I use the firmware update method by turning on the camera via the PLAY button. I've tried every button to gain <ALT> mode, including the PLAY button, but nothing works. When I try to load <ALT> via the PLAY button, the monitor shuts off. When I used the STICK java app to check the firmware version of CHDK to load, it indicated 102a. I downloaded the stable 1.4.1 version of 102a for the G10, and loaded that onto the SD card.
Is there something I can do to load the CHDK menu, or should I try another version for the G10? I don't want to use the experimental versions, as I just bought the camera a few days ago and want to keep it for a while. Also, is it still required to create the FAT16 partition if I want CHDK to boot from the power button later on? My main reason to use CHDK is to allow me to optically zoom when shooting video; the extra RAW options are a welcome addition though the G10 already makes RAW images out of the box.