For those who have been eagerly waiting for information regarding Windows 8.1 and whether or not it will be available in ISO format, today we have good news. The Windows 8.1 Preview will be available in ISO format the same day the update is pushed to the Windows Store, which means you can dual-boot or clean install on any hardware running any operating system.
The ISO will be available from Microsoft directly, however it is unclear where they will distribute them. It’s possible for the ISO’s to be available directly from the Windows 8.1 Preview website, or it a link to the ISO’s will be present on the Windows 8.1 Preview store listing.
Source: MyDigitalLife Forums