Which Chapters are still Valid from Agile Web 2nd Edition

Which Chapters are still Valid from Agile Web Development with Rails 2nd
Edition..?

I would say all of them, but make it into a "what parts of this are
not working" sort of hunt and then when things are not working, scour
the internet for information. You'll probably learn a lot more about
the inner workings of Rails along with the differences between 1.2.x
and 2.x that way than anything else.