It can be run on any machine provided it qualifies.

Yes it is an iso file and you need to D/L either the 32 or 64 bit version. Can't D/L both.

http://windowsupgradeoffer.com/en-GB/Home/ProgramInfo seems to answer your queries although it doesn't mention .iso specifically it does say you can create a dvd so I would presume the files come with instructions to make the .exe into a bootable dvd if .iso is not a choice.

Offer Redemption

Eligible customers must register for the Windows Upgrade Offer through this website by 28 February 2013.

After customer registration and Microsoft validation, customers will receive a registration confirmation email.

Shortly after successful registration, customers will receive an email with a promotion code and instructions for purchasing and downloading the software. The promotion code can be redeemed during the upgrade ordering process to receive the promotional price.

Customers will be able to purchase a downloadable version of Windows 8 Pro. An optional installation DVD is available for an additional fee, plus shipping and any applicable taxes or duties. Customers can also choose to create their own installation media on DVD or USB media after downloading Windows 8.

This offer requires internet connectivity for registering and ordering

Upgrade Software

Each upgrade license will apply to only one PC and may only be installed on PCs with a valid base license to a qualifying operating system (i.e., Windows XP SP3, Windows Vista or Windows 7).

While the offer will be limited to eligible customers who purchase a qualified PC, the upgrade may be installed on any compatible Windows-based PC with a qualifying operating system (see Windows 8 System Requirements). Customers should visit their PC manufacturer’s website for more information on how to upgrade their PC to Windows 8, including updated software and drivers.

Maybe I should have added when you download the files you save them to a folder on your pc, you do not choose to run the upgrade install from the internet.