Also Win 7 has a hidden partition for sys files but think its only a couple of hundred meg.
Also the manufactures of the laptop can have a hidden partition to store the drivers and a uninstalled copy of windows to restore if things go wrong.
the windows 7 hidden partition is more for EFI, when it become more popular I think
Adrian
Desktop machine now powered by windows 7 pro 64 bit, laptop by ubuntu
BTBroadbandanywhere type package, when it works.