Unexpectedly, Microsoft is making thedeveloper preview available to the public today, starting at 8pm PT today. This includes 32-bit (x86) and 64-bit (x64) versions of the OS, with or without development tools, but not any ARM versions, which are chipset specific. Only clean installs are supported, not upgrades from Windows 7.
My expectation was that the initial preview release would have limited distribution and that the general public would get access at Beta.
Based on my early peek at the Windows 8 developer preview build, you're going to want to wait. This build is not stable, and doesn't have the fit or finish of the similar Windows 7 preview from three years ago. Too, it's not feature complete. Instead, this build is aimed squarely at developers. And those users should race to check out what's new.
"The new development tools enable you to start today to build Metro style applications that will seamlessly run on x86 (32 and 64 bit) or ARM architectures," Steven Sinofsky writes in a blog post announcing the release. "Even if you use native C/C++ code, these tools will enable Metro style apps to target specific hardware if you choose. As new PCs become available for testing, PC manufacturers will develop seed programs for developers."
Still not deterred? You'll be able to download the ISOs later today at http://dev.windows.com/. Have fun!