Here is an extract of the iTunes 7 Help :
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Playing albums straight through
Some CDs, such as live concert albums and classical albums, are meant to be played straight through, with no fading between the songs (or tracks). If you turn on Crossfade Playback, you can have iTunes turn it off when you play these albums.
To override Crossfade Playback for specific songs:
In iTunes, select a song and choose File > Get Info.
Click Options.
Select "Part of a gapless album."
Tip: You can select all the songs at once (press Command as you select them), choose File > Get Info, and then choose Yes from the Gapless Album pop-up menu.
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it was not possible before.
a question remains : does it work ?
my answer : not in my short testing course !