MS/ FileSpy and File offset, write position ...

I'm developing a driver for Windows Vista, and I'm new(bie) with Windows.
However, my question is, while I was monitoring the I/O with FileSpy, I noticed that the write to files created byt MS applications did not start at offset 0x0, but from 0x200 (512 bits). When I opened a file with my own c-program, it started from 0x0.
I have tried to find out reason for this, could somebody help me ?
Thanks in advance,
gillespie
[450 byte] By [gillespie] at [2007-11-20 10:15:42]