Different i-pod users on one computer

[Just Gillian]

OH is now the proud owner of an i-pod shuffle. Daughter uses my PC for her massive i-tunes library and has dared me to alter it in any way when I sync OH's shuffle so I'm now frightened to even plug the thing in to set it up and charge it etc

I'd rather not create a new user to deal with OH's device.

Can anyone please explain, in very simple terms, how I set up the new i-pod and upload OH's music without altering daughter's existing library.