Looking for a downloadable windows 7 or vista 64bit

Hey guys. I had windows 7 on my mac, but it was 32 bit, and the game i was trying to play kept disconnecting me because it doesnt support 32 bit. Ive been trying all day to find a good windows 7 or vista thats 64bit. Can someone please link me with a downloadable version, and it must be 4.7gb or under because thats what my disks hold. Thanks 🙂