I looked at
IXUS860/SD870 with 8GB, 16GB or 32GB SD card (=with dual-boot) - SOLVED! and its referenced solutions for sdhc cards. My Powershot S3is natively supported the Transcend 16 gb sdhc card I bought for It. But I wanted the autoboot chdk software to work.
The Stereo Data Maker chdk version includes an installer sdminste.exe that can be used to eliminate the complicated steps for preparing and using your high capacity cards. See
'StereoData Maker' v.1.71 Released for where I got the Idea.
What you need is a working version of CHDK for your particular camera and the file sdminste.exe from the stereo data maker build.
The installer will handle the formatting and switching to and from both partitions and creating the bootable fat12 partition.
Just press the correct buttons on the installer.
Once you have the new card partitioned and both partitions formatted. Copy the latest version of CHDK for your camera model to both partitions on the new card. Use the installer to switch back and forth.
When finished, switch the card back to the bootable fat12 partition. Remove it from your card reader and protect it so it will boot.
To read your photos and videos and transfer the files to your computer. Use the sdminste.exe installer to swap to the FAT32 partition. Your computer will start your download (if it has such software installed) when the FAT32 partition is made active.
After transferring the files from the sdhc card / or (unlocking the card) and upgrading to the latest CHDK build. Swap back to the bootable FAT12 partition (save upgraded files there too if you are upgrading) remove the card and lock it again to set it to autoboot.
hint if you save a copy of sdminste.exe on your sdhc card (in the bootable FAT12 partition, you can run it from the card or copy it to the hard drive of any computer you have access to so you can download you photos when away from your regular pc/pcs.
Best Wishes,
Bernie Bennett