David005 :
But how would I get the correct ISO file on the download tool which is meant for my version of Windows 8.1?
Assuming:
1. You have a DVD with the Win 8.1 on it (Not the Enterprise version)
2. You have access to another PC with a DVD drive
Put the disk in the other PC
Use something (IMGBurn or similar) to create an ISO of that DVD
Use the above mentioned MS tool to create the bootable USB stick
Put that in the PC in question and install.