When an operating system is installed on a hard drive, several sectors at the begining of the drive are written with special information - the MBR (master boot record, where grub usually lives) and the partition table. If the Linux system uses LVM/LVM2 (Logical Volume Management) or software RAID, there is some additional data.
Removing the data on the drive does not change these sectors. Windows can have difficulty interpreting the data in a Linux partition table.
To remove the data, boot a linux rescue disk and type:
dd if=/dev/zero of=/dev/hdx bs=512 count=16
(where '/dev/hdx' is the drive to be completely wiped out)
Windows will now see this as an uninitialzed drive.
Last edited by macemoneta; 06-03-2006 at 01:08 AM.