...can i partition the NAS and put my existing photos on to keep the windows photos visable from all devices?
I doubt you can partition it without erasing it.
do i simply put in a memory card and drag files to the NAS drive in finder? Or can I use iPhoto as normal and somehow point it to the NAS so it saves images there and allows me to view them still in iPhoto from the Mac Mini?
finder copy should work if the Mac sees the NAS. iPhoto won't work with a PC formatted disk as far as I know.