Microsoft is being sued in the US over hardware specifications which it promised were 'Vista Capable'.

The lawsuit (PDF) claims that Microsoft deliberately launched a campaign to stop people delaying the purchase of new computers by certifying them as 'Vista Capable' when they were only able to run Vista Home Basic.

"This consumer class action arises from Microsoft's deceptive and unfair conduct in marketing and selling its new operating system, which it calls Vista, " said the court filing.

"In 2006, nearly a year before Microsoft released Vista, Microsoft began to employ marketing measures designed to avoid a drop in sales of computers incorporating Microsoft's Windows XP operating system.

"Microsoft thus authorised OEMs to place a sticker on PCs indicating that the PCs had been certified as 'Microsoft Vista Capable', meaning that the consumer could upgrade to Vista once it had been released.

"In fact, a large number of these PCs can only run Vista Home Basic, which has been described by one reviewer as 'the most pointless version of Windows ever released'."

The suit points out that Vista Home Basic cannot run the main applications that make Vista so advanced, such as the Aero user interface, and that other features like Internet Explorer 7 are available for Windows XP anyway.

Microsoft chairman Bill Gates is personally accused of deception in the suit for saying on television that users could upgrade for $100, and failing to point out that this too was the cost for only the Home Basic package.

The class action suit, filed for Dianne Kelly of Washington State, is asking for over $5m in damages. Other plaintiffs from within the US have been urged to come forward.