I use the Windows USB tool to create my USB. http://www.microsoftstore.com/store/...usbdvd_dwnTool
You can find links to download the ISO here http://www.mydigitallife.info/window...-home-premium/
Digital River is the official download for folks who purchase a digital copy of Windows 7. These are clean ISOs provided by Microsoft. You can use the same licence number from your physical copy (provided it's not currently installed on something else) or purchase another licence number from Microsoft.