Don't have or know your cam, but try this:
- put an empty file named ver.req or vers.req on your card (plus of course DISKBOOT.BIN and PS.FIR)
- start up in play (not shooting) mode
- press menu, or whatever is needed on your cam to get Canon menu
- firmware update should now be on the bottom of first menu page
that said I now remember there were some cams that did not respond to this, then try this:
get card utility here: zSHARE - cardtricks11.exe
put a card (max. 4 GB ! important) in your card reader and start utility.
check if it is fomatted as FAT (NOT FAT32 !) if not format (it will choose FAT if at all possible)
then click 'make bootable' and lock the write protect tab on the card.
ready, your CHDK should now autoload.
As i said, i'm unfamiliar with your cam, but i think this should work. It is especially important when
starting off with CHDK to experiment first with cards < 4 GB, because Canon cams will by default
format these cards with FAT32, which WILL NOT WORK with CHDK.
good luck, and let us know if this helped ...