bobkn said:
The ISO is free, and available for download.

Windows 10

You won't need a product key if you install it as an upgrade over an activated Win 7 or 8. You shouldn't be asked for one, and it will be activated.

I don't know what your problem might be. The E6600 supports the NX (no execute) bit, and I believe that it has the rest of the required properties. (As others have written, if it runs Windows 8, it meets the requirements for 10, by definition.)
Thanks this route worked for the download portion of the upgrade.