Microsoft has confirmed it has released to manufacturing (RTM) its service pack 1 update for Windows Vista, along with the new Windows Server 2008. However, even users already running Vista will not be able to download the software until mid March at the earliest, while Microsoft tries to address problems with some drivers.

The RTM of Vista SP1 means that the code is finalised, but Microsoft said it will be made available online via Windows Update at roughly the same time it ships with new PCs and is available in retail, expected to be mid March.

Microsoft was expected to make the code available as soon as the RTM milestone was reached, but the software giant said the delay is to address problems beta participants had encountered with some drivers while using pre-release versions of SP1.

"Our beta testing identified an issue with a small set of device drivers. These drivers do not follow our guidelines for driver installation and as a result, some beta participants who were using Windows Vista and updated to Service Pack 1 reported issues with these devices," explained Mike Nash, Microsoft's corporate vice president of Windows Product Management, in a statement on the Windows Vista Team blog.

The solution is simply to re-install the drivers, but Microsoft said the delay will give it time to work with its hardware partners to improve the installation process for the affected drivers.

"As SP1 gets delivered through Windows Update, we will only offer it to PCs that we detect don't have any of the affected device drivers installed," Nash wrote.

From mid April, users that have chosen to download updates automatically will start to get SP1. However, this will not happen if Windows Update finds one of the problem drivers, according to Microsoft. As updates for these drivers become available, they will be installed automatically by Windows Update, after which SP1 will be unblocked and downloaded.

Windows Server 2008 was also released to manufacturing and will be available to purchase on March 1. Volume customers with Software Assurance licensing or an Enterprise Agreement will be able to download it towards the end of February, Microsoft said, as part of the joint Microsoft SQL Server 2008 and Visual Studio 2008 "Heroes Happen Here" launch event.