Did you use a windows
version of fdisk as darin3200
In Linux do
dd if=/dev/nul of=/dev/hdx bs=1k count=1
where "x" in hdx is your actual drive letter.
After that the MBR contains a lot of zeros
I'm not exactly sure about the actual size of the MBR and behind that comes the data for the file system structure. Thus I recommend you do a follow-up reading on this or you do it only when you re-install anyway from scratch. In that case you can change either bs=1M or count=100 to clear any file system remnants. Also