On my external hard drive, from Disk Utility, the 1st partition is FAT32, 2nd is Mac OS Extended, 3rd is ExFAT. I want to use the FAT32 partition to boot on another machine to install Windows on this machine but it doesn't boot. The thing is if I turn that Windows machine's hard drive to external hard drive and create a bootable partition then it is able to boot (this hard drive has two partitions all FAT32). So I guess the problem is my external hard drive with different types of partition. Does anyone know how to make my external hard drive to boot? I have searched a few but my problem is I have only my Mac, no other machines nor more hard drives.
Edit: I want to keep the external hard drive just for booting, and install Windows 8 on the Windows machine's hard drive.