They might be corrupt, but more frequently "cut off in the middle" results from a fault in the download, not in the track itself.
Delete them from your library and download fresh copies at no charge by following this guide: iTunes 10 for Windows: Download previous purchases from the iTunes Store.
In the unlikley event that the new tracks have the same problem, report the matter to iTunes Customer Service.
OK, I see what you mean.
The same album is listed in the USA iTunes Store, and once again tracks 14 and 15 show as 0:00
So, it may in fact be a defective master (which is the thing that I said was "unlikely"!). I see that you have posted a review on the France iTunes Store, but you should go ahead and report it to Customer Service too, using the link provided.
Two weeks have passed. I got reimbursed after the contact with support. Apple still displays the corrupted tracks on iTunes and sells them to other clients.
The peculiar thing is that it is clear that "Apple" is aware of the problem, as they reimbursed me. They even mailed me saying that they are "investigating" the problem. However, investigation apparently does not mean removing obviously corrupt and unusable music.
If you want 0:00 seconds of music for 1 euro, just buy tracks 14,15, 24, 25, 48, 51, 55, 56, 63 or 64 at http://itunes.apple.com/fr/album/bach-matthaus-passion-bwv/id309852339 .