Since Microsoft removed the free download earlier this year they also made some changes to the usb/dvd iso maker. So don't use that. I spent an entire day trying to fix it. If you're using a usb then make sure every usb is unplugged (except your keyboard and mouse) or it will not install. This was a fun problem to figure out.
I used MMOGA but I haven't completed the process yet. So I don't have this as a recommendation. They sent me the old instructions and the wrong w7 download (dell).
http://www.mmoga.com/