I have a sad request... I have Mandrake and XP on the same machine -my wife's machine.. She wants me to remove linux from that machine. Is there a "safe" way to do this without re-installing the OS? Any help would be appreciated.

just use a windows bootdisk and run fdisk and your xp partition will remain untouched ..

Be sure to select to delete non-DOS partitions.

On the other hand
Assuming you dual boot the PC, create a boot floppy (if you don't already have one) then delete the boot loader. Tell the wife that you do not know how to reclaim the disk space then you can still boot linux with out her knowing about it. How to use it without your wife finding out I leave up to you. .

No problem with still using it... I have another box that is running MDK 9.2 quite nicely. Oh, she definately wants the disk space back...

Fdisk won't replace the bootloader with NT loader. You'll need to fire up the recovery console with your XP cd and type "fixmbr". That'll restore the bootloader and she'll get back to XP. After that, you can use XPs nice GUI tool in the disk management snap-in (in the Control Panel, under Administrative services). Just delete the unknown partition (by right-clicking on the pretty box that represents Tuxland) and then choose to format it. If she's picky about having two "drives", you'll have to resize the primary with a 3rd-party (<---read $$$) tool like partition magic and pray that her data is still there when you are done. Good luck. Then, I suggest you let her administer her computer as she sees fit and try to resist helping when she's attacked by a virus, drive-by install, etc. Good luck with that part (my wife didn't like it either)

Assuming I have set up XP/Linux dual-boot using the secondary boot loader method, why does removing the Linux partition with fdisk (perhaps booting the system with Knoppix or another live CD and removing the partition) cause XP not to boot?

I have seen posts to this effect and am confused. Is this because fdisk is changing the MBR?

When you install another OS that OS will ask to write its booting info to the master boot record (MBR) thus over-writing windows info (that it need to boot). The secondary boot loader then takes the job of booting the first installed OS in this case windows. If you remove the partition that holds the secondary boot loader there is nothing left to boot the system. So it is necessary that the MBR be fixed so windows will be able to boot.

cmnorton,
It would of been better if you started a new thread instead of asking your question in a 4 your old dead one.

However, fdisk deletes partitions but does nothing to the Master Boot Record. So as mrrangerman already stated there is nothing to tell grub what to boot and therefore you see the grub prompt ( grub> ) grub can be removed via the windows fixmbr using the windows recovery console.