Well, that is not recommended, as you may regret it soon, but, that's your right :-)
The process consists of two simple steps:
delete all partitions on your hard drive and replace them by a single FAT partition through Managing Your Partitions;
uninstall the bootloader (generally grub) from the Master Boot Record (MBR). To do so, boot under DOS and run the fdisk /mbr command.
If you have another OS, consult its documentation to know how to do same thing efficiently.
Goodbye, and thank you for using Mandrake Linux :-)