How Do You Add Someone Else's ITunes Library To Your Library?

If they paid for them, only they can rightfully play them.  Taking music without paying for it is a violation of copyright law and probably the iTunes user license agreement.  Artists that created the music benefit when listeners play fair.  They lose when people steal their music.

If the songs are on his ipod and you hook it up to your computer it will ask you if you want to sync the ipod select no. You can open the ipod and still copy the songs from it as if they are on his ipod it is assumed they were paid for. If you go to the apple store then you have a different issue.