Step 1. Install iTunes on new machine.
Step 2. Plug in iPod. When iTunes comes up with the message saying something like, "This iPod has been synced to another computer do you wish sync it with this computer" simply press NO.
Step 3. Whith iPod recognised by iTunes Edit -> Preferences -> iPod -> The select update manually option.
To update your iPod now you can import a CD to you lib then manually drag the songs onto your ipod.
If you want to take songs from your ipod to you machine downlaod a utility like iPodAgent