This has been asked many times and you could just search the forum for the asnwer, but since this is your first post i shall make you feel welcome
Go to the Mandrake Control Center, not KDE's or Gnome's...make sure your root, or have roots password, on the side there will be different options..go to 'Boot', then 'Boot Config' and there will be an option to edit your lilo/grub boot manager...select your Windows partition and boot away!
Garry