Windows 7 will be available on October 22nd, 2009. The retail versions (which account for less than 5% of total sales) will be slightly less expensive than the corresponding versions of Windows Vista. There will be at least six versions of Windows 7, but Microsoft is focusing on only three for retail purchases: Home Premium, Professional, and Ultimate. For those interested, here’s a feature comparison page.
Upgrading from Vista will be relatively painless, but Windows XP users will have to perform a clean install of XP before upgrading. This means you are responsible for saving your data beforehand and restoring it afterward. Clean installs are also necessary when converting between 32-bit and 64-bit versions (and vice versa), as well as when you downgrade from a better version of Vista to a lesser version of Windows 7.
Run the Windows 7 Upgrade Advisor to determine if your system is compatible with Windows 7.