Windows 8 has been announced and got excited about the good of computer users. for those who still use windows operating system 7 or vista and xp can install this by upgrade:

win8 Upgrade path to Windows 8, from Windows 7, Vista and XP

Install on:

Windows Developer Preview with developer tools

Windows Developer Preview without developer tools

Windows 7

Clean install only

You can keep accounts, files, and settings

Windows Vista

Clean install only

You can keep accounts, files, and settings

Windows XP

Clean install only

You can keep accounts, files, and settings

A clean install is supported on all builds. You will only receive the full set of installation options when setup is launched in Windows.

Migration of applications is not allowed with the release of Windows Developer Preview, but other options are available to keep your accounts, files & settings in Windows.

Also note that you can’t uninstall the Windows Developer Preview.

To reinstall your previous operating system, you must have to restore or use installation media again.