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The article below may be able to help you with this. Click on the link to see more details and screenshots.
The steps involve creating USB media containing the current Boot Camp Windows Support Software (drivers) for you to connect to your Mac during the install process.
- In OS X, choose Utilities from the Go menu.
- Open Boot Camp Assistant.
- Click Continue.
- If you are using a downloaded copy (ISO) image of Windows 8, click the checkbox next to "Create a Windows 7 or later install disk" so it has a checkmark in it.
- To install Windows, click the checkbox next to "Install Windows 7 or later version" so it has a checkmark in it.
- To create USB media that contains the ISO installer and the correct drivers for your computer, click the checkbox next to "Download the latest Windows support software from Apple" so it has a checkmark in it.
- Click Continue. You'll be asked to attach the USB media (flash drive or hard drive) that the Windows Support Software (drivers) can be installed on. Caution: All data on the USB media will be erased during this process. Follow the onscreen instructions to complete the creation of the media. If you want to create your own driver installation media without using the Boot Camp Assistant, click here and follow the instructions on the download page.
- Follow the onscreen instructions to complete the Windows 8 installation. For more information, see the Boot Camp 5 Installation Manual.
I hope this information helps ....
Have a great day!