Exactly the same situation here. I bought my Digital IXUS 80 IS (other name for the PowerShot SD1100 IS) in New Zealand in February 2009. The firmware is also 18.104.22.168. So I've tried the CHDK versions for firmware 1.01A and 1.01B. They both boot fine and seem to work, the menu is accessible. I've done more tests with CHDK for 1.01A (a few long exposures, changing some options, playing the games...), and everything works fine for the moment.
Hope it helps.