How do I open that files from a recorded CD?

With the application that originally saved them.

CurlyBen is right. . dat files are not typically "readable" like .doc files would be.

More info:

These are raw data files of some kind. The ONLY program that can safely use them is the original program, in most cases. You can open one of them w/Notepad and you will see why. Generally the raw data is meaningless to the human eye.

In rare instances you will find a conversion tool that may be able to utilize them, but again, you need to know what program originally created them before you'll be able to search for a candidate conversion tool.