You could set it up so your brother has a different iTunes library. To do this, hold down shift while clicking on the iTunes icon. You'll then be presented with the option of choosing a library. Set up a new library for your brother. Close iTunes and perform the "shift click" when selecting iTunes again to choose your own current library. Just remember that after you use iTunes you should be sure to shift click iTunes and choose your bro's library then exit again, so that way when he connects his iPod it'll go directly to his library and not yours.
