Some PC vendors and sellers will begin a coupon programme on June 26 to entitle people who buy premium versions of Microsoft Windows Vista to upgrade to the new Windows 7 operating system when it arrives later this year, but the upgrade offers may not be free. Offers will vary by vendor and retailer.

Three Taiwanese PC makers plan to provide a coupon for a free Windows 7 upgrade to anyone who buys a new desktop or laptop PC loaded with Vista Home Premium, Vista Ultimate or Vista Business between June 26 and the time Windows 7 launches globally on October 22, according to executives from the companies. They requested not to be named in this story for fear of harming their business relationship with Microsoft, because the software giant has not yet announced the timing of its Windows Upgrade Option (WUO) programme.

PC vendors will have to pay between $9 and $15 per PC to include an upgrade coupon with a new computer, said an executive at one Taiwanese PC maker. People will use information on the coupon to download a copy of Windows 7 from a Microsoft website once the software is on sale, he said, and Microsoft will also send the holder a copy of the operating system on a disc.

Another executive said the upgrade coupons will be good from June 26 until January 31, 2010 and are meant to encourage people to buy new PCs ahead of the October 22 launch date for Windows 7.

PC makers fear consumers and businesses may put off buying a new desktop or laptop until Windows 7 formally launches in October, causing a downturn for PC sales this summer. The upgrade programme is aimed at keeping PC sales steady over the time.

Microsoft has not announced a date for when its Windows Upgrade Option programme will begin, said Amelia Agrawal, director of public relations at Microsoft Asia Pacific, in Singapore. However, she pointed out that the upgrade offers will vary by PC manufacturer and retailer.

A Taiwanese executive also said he feared the upgrade programme will hurt sales of netbooks because they come with Windows XP instead of Vista. Netbooks are among the hottest sellers this year for PC makers due to their small size, long battery life and low-cost. But XP users will not be offered an upgrade coupon.

Information from the Taiwanese executives matched most of the information in a memo from US electronics retailer Best Buy, leaked last week.

Several companies in Taiwan plan to offer Windows 7 upgrade programmes, including Acer, Asus, Gigabyte Technology, MSI, and Shuttle.

HP will participate in the Windows Upgrade Option programme but won't disclose details until Microsoft formally announces the start date, said Ann Finnie, public relations manager in HP's personal systems group.

Chinese PC maker Tsinghua Tongfang will not offer upgrade coupons since few of its machines offer eligible versions of Windows Vista, a company representative said. She said she did not know the launch date of the programme.

(Owen Fletcher in Beijing contributed to this report.)