That's called ripping, to get music (or spoken text in case of books) from the CD to mp3-format. Windows Media Player does it. And you can find other programs that do it also, like CDEX (free).

A CD is 700 MB. A music mp3 is about 1 MB per minute. For spoken books you can lower the quality (if your ripping program allows it) so it's only 0,5 MB per minute.

1 MB a minute = 8000 minutes in 8 GB = 133 hours to listen to in 8 GB. That's enough?

Kees