I just have installed iTunes 9 to see what might have changed, but it is still the same.
1. go to iTunes Preferences > General > Import Settings (down by the When you insert a CD action selection field) > WAV.
2. Select the .mp3/.aac/audio file(s) you want to convert, go to Advanced (Menu Bar) > Create WAV version.
Is that not available for you?
Maybe the songs you want to convert are copyright protected.