That seems to be a cumbersome approach. It means that two CHDK versions have to be maintained including scripts or so.
Not very cumbersome - I'm currently using SmartSync and it keeps track of file/folder changes on the SD Card and automatically copies them to my hard drive. No matter which SD card or which partition I use, it is automatically checked against the latest changes on my computer and updated if needed. If a file on my computer needs updating by a newer change on an SD card, then it gets updated. An advantage of using an app like SmartSync is that when SD cards start slowing down after a lot of use (defragmentation) and they need to be reformatted to speedup the saving of photos, then SmartSync takes care of copying the files and folders to the SD Card after reformatting.
I don't know about the SX20 but a very easy tool to use a card with more than 4GB is SDM Installer (Stereo Data Maker) found at http://stereo.jpn.org/eng/sdm/download.htm
I never used SDM for its stereo purpose but for downloading the pictures and setting up the card.
Instructions on how to setup everything can be found @ http://stereo.jpn.org/eng/sdm/quick.htm
The SDM Installer is mentioned in the posting I referenced for the tutorial to setup the 4G cards (
http://rapidshare.com/files/400436852/Installing_CHDK_on_SD_Cards__Windows_OS_.pdf).
Several advantages of the 4G dual, bootable partitions are:
1 - Under the previous dual partition setup Windows users need to remove the SD card, swap partitions using SDM Installer, unload , swap partitions using SDM Installer, and then put the SD card back in the camera. With this dual 4G setup, you simply remove the SD card, unload, and put the SD card back in the camera. You don't need the SDM Installer during this process, you avoid two partition swaps,
and you can upload to a computer that doesn't have the SDM Installer installed.
2 - You can do USB to PC transfers from either partition (JPGs and movies - still not DNGs, etc.)
3 - You can keep different events on separate partitions without swapping SD cards (i.e. wedding vs reception photos). The SX20 CHDK estimates show each 4G partition can have approx 1205 JPGs (fine mode) or 180 DNGs (with accompanying JPGs - fine mode) - plenty of room on each 4G partition.
4 - After one 4G partition starts slowing down due to defragmentation, you can swap to the other "fresh" partition.
BTW this should have been posted in a different section.
The section heading read "Creative Uses of CHDK - Report a new way to use an existing feature, new discoveries, etc.", so that's why I thought this was the correct section.