Trevor, can you check the link, it doesn't appear to work, I get a page load error ; "Firefox has detected that the server is redirecting the request for this address in a way that will never complete."
I was able to install the CHDK on my A550 after a couple of false starts.
This is a better website: http://chdk.wikia.com/wiki/CHDK
I had problems getting back to the other site. This one has a more complete download package.
You need to read the FAQs and Readme files carefully.