Thinking of upgrading to Windows 7? If so, you should read this article by Microsoft.
This document outlines supported and unsupported upgrade paths for editions of the Windows® 7 operating system.
Unsupported Upgrade Scenarios
• Upgrades to Windows 7 from the following operating systems are not supported:
• Windows 95, Windows 98, Windows Millennium Edition, Windows XP, Windows Vista® RTM, Windows Vista Starter, Windows 7 M3, Windows 7 Beta, Windows 7 RC, or Windows 7 IDS
• Windows NT® Server 4.0, Windows 2000 Server, Windows Server® 2003, Windows Server 2008, or Windows Server 2008 R2
• Cross-architecture in-place upgrades (for example, x86 to x64) are not supported.
• Cross-language in-place upgrades (for example, en-us to de-de) are not supported.
• Cross-SKU upgrades (for example, Windows 7 N to Windows 7 K) are not supported.
• Upgrades from Windows Vista to Windows N, Windows K, Windows KN, or Windows E are not supported.
• Cross-build type in-place upgrades (for example, fre to chk) are not supported.
• Pre-release in-place upgrades across milestones (for example, Windows 7 RC to Windows 7 RTM) are not supported.