Apple released a beta/developer preview of Mac OS X 10.7 to developers.
To install und use the beta you must have a developer account and a Mac with Intel Core 2 Duo or better.
You can also install Lion 10.7 on older Macs by simply deleting a plist located here:
"
/Volumes/Mac OS X Install ESD/System/Library/CoreServices/PlatformSupport.plist".
Some russian users from AppleLife.ru have successfully installed Lion on a hackintosh.
The only thing is that you have to boot Mac OS X 10.7 with an old Bootloader called "XPC".
And of course as of now you can only use Lion on Intel CPUs and without Chameleon Bootloader because it will not boot 10.7
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