Acer claims the real purpose behind the proliferation of different Vista editions is that Microsoft wants to effectively raise Windows prices by 10 percent.

The most basic version of Vista, Home Basic, will cost around the same as the Home edition of Windows XP. But the software is so stripped-down that many PC makers, including Acer, are not even planning to offer it. That leaves Home Premium as the lowest tier, according to Acer senior corporate vice-president Jim Wong.

The quandary for PC makers is that Vista Home Premium, the next version up, costs 10 percent more for manufacturers than XP's Home edition. That is such a big jump that it adds one to two percent to the overall cost of manufacturing a PC, in an industry where margins are already wafer-thin.

Wong believes consumers will demand Vista Home Premium but will not put up with higher PC prices, leaving manufacturers to absorb the extra costs.

Earlier this week, Microsoft admitted that some PC users will be put off by licensing enforcement measures built into Vista. Company spokesman Mike Burk said Microsoft users who frequently change the hardware configuration of the system running Vista may fail Vista's new Software Protection Platform software-validation feature more than once. If they did, they would be required to purchase an additional licence or use Microsoft's support services to activate Vista on a newly configured machine.

And an expert in software migration this week said there are even fewer reasons for businesses to upgrade to Vista than there were for upgrading to Windows XP. Rich Bentley, client and mobile manager for software developer Altiris, also attacked some market researchers for over-optimistic forecasts, in particular Gartner and IDC figures, which suggest that Vista could be in mainstream use by the end of 2007.