you can find the first beta version of the Ixus 55 / SD450 port of CHDK at the following location:ixus55_100b.zip - 1.97MB
(link updated, see below)
Please note that not everything is working yet. Especially raw-capture still leads to a shutdown of the camera. Also zebra mode is still not working correctly. Since I do not have the time to test everything (and frankly I have not used every funtion to be able to test it properly) I would like to share the current status-quo of the port so that others can use it and improve it.
Thanks to GrAnd and ewavr for helpful suggestions. I also learned a lot from the Ixus 70 port by quietschi due to the many helpful comments in your code, thanks for that as well ;-)
Let me know if you find any bugs...