there is a (previously) undocumented option in the plain old fdisk program that comes on the venerable old windowns 95/98 bootdisk. fdisk /mbr should wipe out the master boot record on your hard drive and leave future winOS installers clueless as to the previous existence of any older OS'es you had on the disk.
From the MS website:
http://support.microsoft.com/kb/69013"SUMMARY
The MS-DOS Fdisk utility usually updates the master boot record (MBR) only if no master boot record exists. Repartitioning with Fdisk does not rewrite this information.
Fdisk has an undocumented parameter called /mbr that causes it to write the master boot record to the hard disk without altering the partition table information.
Warning Writing the master boot record to the hard disk in this manner can make certain hard disks partitioned with SpeedStor unusable. It can also cause problems for some dual-boot programs and disks with more than four partitions."
