Use a DOS 6 or above floppy with fdisk.exe inside.
Boot it up and type
If you haven't got such a floppy download one from bootdisk.com.
If you haven't got a floppy drive, download FreeDos and burn it into a CD, as it has fdisk.exe inside. Just do it same way as a DOS floppy.
Otherwise live with the MBR left by Mandrake. It couldn't harm you.
The problem is likely due to the partition being formatted and not the whole hard disk.