Question about ipod connection to pc?

OK so the other day my girlfriend brought her iPod touch 4g over so i could give her some of my music. All I had to do is plug it in and drag albums into it and it worked. However, I tried giving my brother some music and it asked me if i wanted to erase and sync/ authorize to play transferred purchases etc. I canceled the sync and dragged the music to his iPod and a little � sign popped up and wouldn't let me. Is there some option on the iPod or my brother's native itunes account that i can select so that it just allows it like my girlfriend's iPod does. (They are both iPod touch 4g's. My brothers is 8GB and gf's is 32GB if that matters...)