just out of interest do the drivers work?
reason I ask is that I have a canon ixy 320 (japan model) hooked up to my gentoo and with gphoto2, libgphoto2 and gtkam I don't get to choose my exact model - I get IXUS v3 on autodetect and it works fine
actually I notice that IXUS 400 is in my list of cameras too - perhaps try compiling the 3 items above from source (???)
I don't know what additional features the newer IXUS/IXY has, but from my own experience (parents have a 200-series) the numbering is more to do with the pixels rather than additional functionality - digicam buffs feel free to tar and feather me now
if you're dead set on using the model-specific drivers, try either the rh update (if it still works) or google for the packages listed above -
here's a starter for 10
hope you get it working