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Thanks for the info! This solved the USB keyboard problem I was having. However, for those not comfortable with downloading drivers from the linked site, you can extract them from the Boot Camp 5.1.5621 download found here: https://support.apple.com/kb/DL1720?locale=en_US

Once you extract the file, the necessary driver is found under the path: BootCamp5/BootCamp/Drivers/Apple/AppleKeyboardInstaller64.exe
 
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