First back up the contents of the hard drive of your Mac.
Browse to Application and click Utilities folder and then double click to open the Boot Camp Assistant on your Mac.
Choose a size to partition your drive. This will be how much room you have on the Windows side of your Mac. Choose this number based on if you're planning on playing a lot of games, or just running a few programs. It is better to allocate 25GB of space to Windows 7 in order to avoid frequent crashes of programs.
Click on the "BOOTCAMP" partition, click "Options," and then "Format." Click "OK" in the following dialog box. When it's done formatting, click the "BOOTCAMP" partition again, and install Windows on that partition.
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