External USB HDD : files disappeared

[rudu <rudu@cegetel.net>]

Hi,
A friend of mine recently experienced a loss of data on his 500G 
external WD drive.
Quite inexplicably, some directories became empty, some file sizes 
became null while others stayed intact.
df -h
Sys. de fichiers    Taille  Uti. Disp. Uti% Monté sur
[...]
/dev/sdb1             466G  196G  270G  43% /media/My Book

du -sh /media/My\ Book
32G    /media/My Book

fdisk -l
Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x44fdfe06

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1       60801   488384001    c  W95 FAT32 (LBA)

What I tried :
Photorec : the renaming of restored files would take years, not an 
option for my friend ...

Testdisk : No need to partition recovery here, the "Repair FAT" option 
only states that everything's OK.

dosfsck -v /dev/sdb1 : shows a lot of " Start does point to root 
directory. Deleting dir."
I suppose it's going to wipe out all incoherent result.

I'd suspect the FAT file system for having messed something for some reason.
Is there any chance to restore the FAT tables or to reconstruct them ?

Thanks for any help.
Jean-Marc