Okay, we fixed it. We did two things at the same time, so I am not sure which it was, but I flushed "/etc/blkid.tab" by doing a:
cat /dev/null > /etc/blkid.tab
(after backing it up of course)
and I also changed his fstab line:
/dev/hdb1 /mnt/Windows/ ntfs auto,user 0 0
/dev/hdb1 /mnt/windows/ ntfs default,user 0 0
Thanks for your help guys!
I meant "foolishly" as in trying to check it as an ext3 file system.