In iTunes 6 and earlier, the iTunes navigation-bar contained a Library playlist that listed all the audio and video in your iTunes library. iTunes 7 removed this, and segmented the library into various libraries (e.g Music, Movies, TV Shows).
You can enable the general iTunes Library, quit iTunes and type the
following two commands:
defaults write com.apple.iTunes show-library-playlist -bool TRUE
defaults write com.apple.iTunes hide-library-playlist -bool FALSE
To disable the general iTunes Library:
defaults delete com.apple.iTunes show-library-playlist
defaults delete com.apple.iTunes hide-library-playlist