Apple also mentions the versions of Windows 7 you will need if you want to install a 64bit OS. Apple also lists the exact Mac models compatible with Windows 7 (64-bit). This is also mentioned in Apple”s manual for Boot Camp 4.0 for Lion. Make sure you disconnect all USB devices except a wired keyboard and the USB drive containing the Windows ISO files. To install Windows OS on Mac without Boot Camp, you should let your Mac booting from USB drive to start the installation process.
Mac will boot from internal hard drive or SSD in default.
