Windows – BOOTCAMP | No choice to locate ISO

You can do this using macs built in DiskUtility.app.

Insert the Windows installation DVD into the external Superdrive.

Open Disk Utility, Select the USB optical drive in the left DiskUtility window.

Click new image in the top bar.

Select DVD/CD master from the "Image Format" submenu. Choose "None" for encryption.

After the image is done, locate it in Finder and highlight the file. Press enter/return and rename the disk image file extension to .iso

Eject the Window installation DVD and insert your USB that is FAT32 formatted and use Master Boot Record for the partitioning scheme.

Open up Boot Camp Assistant and make sure "Create a Window 7 or later version install disk" is checked. When you click continue it will prompt you to select the location of your .iso file you created.

Link to Apples Guide for creating a Windows .iso for BootCamp

I found the culprit. It seems the Apple HFS driver isn't compatible with Windows 8.1. I booted a rescue disk and removed the AppleHFS.sys and AppleMNT.sys files from C:\Windows\System32\drivers and rebooted, and Windows 8 booted fine.

I obviously lose the ability to have read-only access to my Apple filesystems, but this is not a big deal to me because since I work on a lot of Windows boxes anyway I use external ExFAT-formatted SSDs and flash drives to transport data around.

For others, if having some sort of HFS access was a deal-breaker, there are other solutions out there that can mount HFS partitions. Can't think of any, especially that are free, but in any case, at least Windows now boots on this machine and works as expected.