Microsoft's first service pack update to Windows XP is now available for download.

The service pack to Microsoft's latest operating system sports dozens of security and bug fixes, additional driver support and interface changes, plus one minor change to the Windows XP activation feature.

For corporate customers wary of initial releases the appearance of a first service pack often represents a green light for upgrading. But the debut of Service Pack 1 may be insignificant for home and small office users, especially if they have kept their versions of Windows XP up to date through the Windows Update site.

However, Microsoft has also modified its controversial Windows Product Activation antipiracy mechanism with a small but welcome change. The Windows Product Activation function was intended to prevent customers installing the same copy of the OS on several PCs by checking certain hardware specifications. Many users were concerned that upgrading their system memory or adding hardware would prompt Windows XP to assume it was running on a new PC and lock them out.

Microsoft has now altered the Activation feature so that if Windows XP detects changes that may indicate installation on a new system, there will be a three-day grace period before it locks up your machine. The alteration is intended to prevent unexpected hardware changes from rendering a legitimate PC installation inoperable and gives users a few days to contact Microsoft by phone and assure the company they just have a new motherboard, not a new PC.

Service Pack 1 provides additional support for Microsoft's still-emerging .Net web services platform and for new hardware platforms including Windows XP Tablet PC Edition, Windows Powered Smart Displays and XP Media Center Edition.

Other elements, such as the restoration of Microsoft's Java Virtual Machine (which Microsoft says it removed from Windows XP due to a Sun lawsuit) are unlikely to arouse much interest from the average Windows XP user. The service pack also includes interface changes meant to satisfy government antitrust lawyers.

In addition, SP1 includes support for USB 2.0 devices — an enhancement already available as a downloadable add-on from Microsoft's website.

The 133MB Windows XP SP1 is downloadable here.