Now you can download an ISO file and install it yourself.
Windows 8.1 Preview (English) 64-bit: WindowsBlue-ClientwithApps-64bit-English-X1899605.iso
SHA-1 Hash: 0xD76AD96773615E8C504F63564AF749469CFCCD57
Windows 8.1 Preview (English) 32-bit: WindowsBlue-ClientwithApps-32bit-English-X1899604.iso
SHA-1 Hash: 0x8BED436F0959E7120A44BF7C29FF0AA962BDEFC9
PRODUCT KEY: NTTX3-RV7VB-T7X7F-WQYYY-9Y92F
If you are running Windows 8, simply double-click on the ISO file and run Setup.exe. If you are running an older version of Windows, you will need to either burn it to a DVD or create a bootable USB installation.
Important: Windows 8.1 Preview isn't currently supported on some tablets and PCs with newer 32-bit Atom processors.
If you need ISOs in languages other than English, look here.