Technically, you CAN recover music off of an iPod back onto a computer, but this is a hack through 3rd party programs, which you can download for free. I would recommend backing everything up onto CD anyway.
Easiest way through iTunes-
In your preferences, set your burning preferences to 'Data CD'.
In your main library, select 'All' from the 'artists' list window and drag it into your playlists window. This creates a new playlist of everything you own. When you go to burn this playlist, it will fill one CD and automatically ask for another disk until you are done.
I Assume you are going to pack up your computer in its original box and wrap 40 or fifty pillows and trash bags around it with duct-tape, right? 😀