According to ZDNET, Microsoft has detailed its Windows 8 upgrade plans to select partners. The news is mostly good: Windows XP, Vista, and 7 customers can all upgrade to Windows 8, but there are some restrictions. Here's how it plays out:

• Users running Windows 7 Starter, Home Basic, or Home Premium can upgrade to Windows 8 with their system settings, personal files, and applications intact.
• Users running Windows 7 Starter, Home Basic, Home Premium, and Professional will be able to upgrade to Windows 8 Pro with system settings, personal files, and applications intact.
• Customers running Windows 7 Pro or Enterprise editions can update to Windows 8 Enterprise with system settings, personal files, and applications intact.
• Vista users without SP1 can upgrade to Windows 8, but only personal files will be preserved. Customers that do have SP1 will have their system settings transferred as well.
• XP users with SP3 can upgrade directly to Windows 8, but only personal files will be preserved.

There are a few more specific restrictions, like cross-architecture upgrades — 32bit XP, Vista, and 7 users can only upgrade to 32 bit Windows 8, and likewise for 64 bit Windows. Upgrading to a new language also bars system settings and applications from being transferred, but personal files will remain unaffected. This leaves current XP, Vista, and Windows 7 users several upgrade options, and with an expected October release date, there is still plenty of time to prepare.