I am having a dual boot of Windows 2000 and RedHat Enterprise Gnu/Linux ..
I feel, its a good idea to go for Windows installation first .. So that you dnt have to manually do anything with the Windows Loader .. I am not entering into the details, neither I know much abt that ..
So, if u install Windows first and then go for Mandrake GNU/Linux, u will have to go for a Boot Loader .. This Loader will be responsible for the Option Menu .. This Option Menu will be a screen before ur system boots up .. In this option menu, u can select between Windows and GNU/Linux as it will show both of them as options .. I guess Mandrake will be giving u two boot loaders to choose from GRUB and LILO .. I have used both and they both seems to be fine ..
You can also configure ur Boot Loader to make any of the OS as default .. So that after an interval of few seconds, it will load the default if u won't select ur choice ..
For partitions, first go for windows partitions (14 GB in total for u ).. Either, don't format remaining space or even if u do, u can always reformat it when u install Linux ..
Feel free to come back for any clarifications on the same ..