PCs from Hewlett-Packard, Gateway, Lenovo, and other major computer makers that contain a widely used Intel chipset can't be upgraded to Windows Vista Service Pack 1 if they're running certain drivers.

Microsoft has said that Vista SP1 won't work with "a small number of device drivers." The list, however, includes drivers for an Intel chipset that's found in thousands of PCs and laptops.

The affected chipset is Intel's 945G Express series, which is used in computers from virtually all major system vendors. It's also found on standalone motherboards sold by Asus. The 945G Express chipset driver versions between numbers 7.14.10.1322 and 7.14.10.1403 won't work with Vista SP1, according to Microsoft.

Chipsets provide a connection point for all key subsystems within a PC.

The 945G Express chipset includes Intel's GMA 950 graphics core, which also won't work with Vista SP1 if those drivers are used.

Microsoft is urging Vista users to update all of their hardware to the latest drivers before even attempting to install SP1.

The service pack also won't work with computers that use certain, widely-deployed audio drivers from Realtek and certain drivers for security devices manufactured by Symantec. Microsoft has published a full list of drivers that are incompatible with the service pack.

Meanwhile, Microsoft is continuing to receive reports from computer users who say Vista SP1 is wreaking havoc on their systems.

A user going by the name "Apolauf" said the upgrade caused the mouse cursor on his tablet PC to disappear. The "right-click circle and the special pen mouse cursor ... are no longer functional" as well, said Apolauf, in a post on the Vista team blog.

Bob Rife, a user from Canada, said in an e-mail to InformationWeek that SP1 caused one of his computer's two hard drives to become invisible to Windows Explorer and Acronis Disk Director. Rife said he complained to Microsoft, but has yet to receive a response.

Others reported having no problems. A user named "Zandor" said on the Vista team blog that his company successfully upgraded 614 computers to Vista SP1. "Great job, Windows team," wrote Zandor.

Microsoft made Vista SP1 widely available for the first time on Tuesday. The update includes more than 300 hot fixes designed to improve the operating system's speed, security, and stability.