"You can also use Custom if your computer doesn't have an operating system , or if you want to set up a multiboot system on your computer."

I must say, that IS a bit confusing. I fail to see how you can run the .exe file without an operating system. I expect that you have to create a bootable DVD, and launch the executable from there. Just burning the files on a DVD will not get the job done. BTW, of the three files you listed, just run the Win7-P-Retail-en-us-x64.exe and everything is automated from there.