you can install windows on to a drive on your mac, just not with boot camp.
there will be some problems to get past in use as windows wont be able to see your osx drive so dont set windows as the default drive unless you want to mess around.
install windows with a DVD drive to save problems (USB can work but will give problems later potentially)
to install pull all drives and PCI card apart from one GPU and destination drive for windows
put in dvd to drive and install win
once install done update & install drivers
then you can re insert all your HD's and pci cards
thats how i last did it at least ^^, like me hope you dont need to reinstall and think about imaging your fresh install if you ever want to save time
edit ops im to slow to post
don't try to install win on to the same drive as osx & if you do get stuck in windows you can also just pull the win drive or use a original mac gpu and alt startup