Microsoft said Tuesday that it's resumed distribution of a prerequisite file for Windows Vista Service Pack 1 after fixing a bug that caused some users' computers to enter a cycle of reboots during installation of the file.

The fix applies to Microsoft's Servicing Stack Update for Vista SP1. Users need to install the update before downloading SP1.

"This fixes an issue that a small number of customers experienced when we first issued the SSU in February," said a Microsoft spokesman.

Microsoft said it plans to start distributing Vista SP1 in five languages, including English, in mid-April through its online Automatic Update system.

Microsoft made Vista SP1 available to some developers and commercial users as a download from its business Web site last month. It's also been slipstreamed into boxed versions of Windows Vista now available from Amazon.com and other retailers.

Vista SP1 contains a number of features designed to enhance the operating system's speed, performance, and stability. Among other things, it offers a patch that will allow users to run the BitLocker encryption tool on multiple hard drives. It also improves the speed at which the OS wakes up from "hibernate" mode.

SP1 also will remove from Vista the so-called Kill Switch -- a feature that deactivated key components of the OS if Microsoft detected users were not running a properly licensed copy.

The feature was plagued by false alarms that flagged thousands of legitimate Vista users as software pirates.

Vista SP1 itself isn't without problems, however.

Microsoft has yet to finish ensuring that the service pack will work properly with the thousands of models of keyboards, printers, mice, and other peripheral devices commonly attached to personal computers.

Such peripherals use bits of software called drivers to communicate with the host computer.

The problem is that Vista SP1 won't install some device drivers correctly. Microsoft says the issue is confined to "a small number" of drivers and that it's working on the problem.

Microsoft hopes Windows Vista SP1 will quell some of the disappointment that greeted the operating system's initial rollout early last year. Many business and home users complained about its resource requirements and lack of compatibility with existing applications.