If you have three computers in your family, all running on Windows XP or Windows Vista, you might want to upgrade using Amazon's Microsoft Windows 7 Home Premium Upgrade Family Pack offer.
At £108.04 including VAT and delivery, it contains a single license for Windows 7 Home Premium that can be installed on up to three computers, that's a mere £36.01 per seat, less than a third of the price of the full version and less than half the price of a SINGLE license.
No wonder therefore that it is currently the best selling operating system at Amazon and Microsoft is discontinuing it probably because it is so successful.
The pack contains both the 32-bit and the 64-bit versions of Windows 7 on a single disc making installation a doddle and you may swap between the two at any time.
It is possible to do a clean install of Windows 7 Home Premium Upgrade on a clean, formatted hard disk drive although it is essential, for legal reasons, that you do have the appropriate certificate of authenticity.