You're going to join a 3.5 game. In order to restrict minmaxing and bloat, the DM has given a caveat: You have access to only core books and ONE expansion book. Only you get to use the spells, classes, treasure, feats, etc from that book (although other players can also opt to choose the same book as you).
Books that are off limits: Spell Compendium and Magic Item Compendium. Those are in the province of the DM and he or she may decide to use part or all of the things from those books.