Need help giving Items an Item class.

ok, so I make an Item Class (or three of them), name it (them)...
Then I make a new Item... the object editor window that pops up when I add object in the Items tab has a drop down menu for Item Classes.. but when I click it, nothing dropps down, and no Item Classes are listed at all.
every tutorial I see acts like you can select an Item Class here so I assume it's an implemented feture.. so what am I missing?