The Home Premium Edition is on sale through the site for the budget price of £66.99 exc. VAT (£78.71 inc.). What's more the Ultimate Edition is on offer for £114.99 exc. VAT (£135.11 inc.).
That's a significant saving on the retail versions. Before withdrawing the price, Amazon had Home Premium slated at £219 and Ultimate at £349 - these are for full versions, not the cheaper upgrades.
When questioned, Microsoft responded to us with this statement:
"The units that are being sold on Overclockers are system builder copies designed for people building PCs."
"Microsoft made copies available so that our assembler community has time to build PCs ready for sale on 30 January 2007. However Microsoft did not authorise Overclockers to sell any copies."
The legality of OEM copies has always been a slightly hazy issue. The practice of selling OEM copies of operating systems really reared its head in 2004. Sites started selling OEM copies of Windows Media Center 2005 by bundling the OS with a piece of hardware, such as a TV tuner card.
There was another reason for that happening with Media Center - so it could be installed alongside a TV tuner card that actually worked with the operating system. However, there are no such hardware offerings alongside these OEM versions of Vista.
Microsoft has traditionally turned a blind eye to this practice and from its comments looks set to do so again. Amazon has recently been selling OEM copies of XP that offer a voucher upgrade to Vista when available.
If you do install an OEM copy of a Microsoft OS, bear in mind you won't get any support. That's because support is up to the system builder. In this case, it's you.
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Dan (Twitter, Google+) is TechRadar's Former Deputy Editor and is now in charge at our sister site T3.com. Covering all things computing, internet and mobile he's a seasoned regular at major tech shows such as CES, IFA and Mobile World Congress. Dan has also been a tech expert for many outlets including BBC Radio 4, 5Live and the World Service, The Sun and ITV News.