Microsoft Store has Windows 8 Pro Upgrade as a download for $39.99 for limited time. Deal expires January 31, 2013.

If you currently have a personal computer running Windows 7, Windows XP or Windows Vista then you can upgrade to Windows 8 Pro (Professional). With Windows 8 Pro, you can connect and share your files. Windows 8 Pro also adds enhanced features if you need to connect to company networks, access remote files, encrypt sensitive data, and other more advanced tasks.

The Windows 8 Pro Pack enables you to move up to Windows 8 Pro from Windows 8 Standard. The Pro Pack makes your PC or tablet ready for business by adding prifessional-grade features like BitLocker for encrypting your data, SmartScreen, Remote Desktop, and Windows Media Center.