No, you don't need to sign up as a beta tester to try out Windows — anyone can install and test drive the Windows 8 Developer Kit.
http://msdn.microsoft.com/en-us/windows/apps/br229516
You can grab it in both 32-bit and 64-bit flavors, or the 64-bit version along with developer tools. The developer tools version requires a clean install, but if you have a Windows Vista or 7 installation on your machine, you can keep accounts, files and settings with a new installation. Windows XP users can upgrade and keep their accounts and files only.
Good for home users but for office work VERY counter-productive.
But lockscreen is pretty awesome indeed.