SP1 tackles reliability and performance, adds support for new hardware and incorporates the earlier updates for compatibility with third party software. Microsoft claims more than 2,000 applications are now "certified for" or "work with" Windows Vista.

Now the catch... A number of security products won't start up or run on updated desktops thanks to "compatibility problems". Among those affected are BitDefender AV or Internet Security, Fujitsu Shock Sensor and Zone Alarm Security Suite. Meanwhile, other products will experience "loss of functionality" once you've installed SP1, Microsoft have said. Click here for more details from the Microsoft knowledge base.

Microsoft has also introduced a number of security changes to Windows Vista, including updates to BitLocker drive encryption. SP1 is "aligned" with Windows Server 2008, the two operating systems sharing common files in Internet Information Services and concurrent user support.

The first Windows Vista SP has long been seen by some as the catalyst for broad uptake of the operating system among businesses. Especially as XP will not be available to purchase from June 2008.

You can now download the new Service Pack here. However, many Vista customers have been complaining about problems with installing Microsoft’s first service pack.

Vista Ultimate customers with the language packs in English, French, German, Spanish and Japanese are among the privileged few who can download the service pack. Other versions have been reported as being unable to download the update.

According to the official Vista team blog, as well as elsewhere on the interweb, plenty of frustrated customers are wrangling with the manual version of the service pack.

One poster regretted installing SP1 after spotting its availability on the WU site. “In retrospect, not my finest decision,” said SeppDietrich. “What a disaster! It exiled all of my Nvidia drivers to the Bermuda Triangle... they're simply all GONE.”

Microsoft has acknowledged that the service pack will not install on computers that use “incompatible” peripheral device drivers from the likes of Realtek and Intel. However, there’s no mention of known problems with Nvidia drivers on Microsoft’s rather long list.

Other complaints about the service pack included sluggish response times, random crashes, and one from a puzzled Aussie who was told his language wasn’t supported for his Vista Ultimate-loaded PC.

The firm hopes to address this next month, when the real test for Vista SP1 begins in earnest as it is finally pumped out automatically to the masses.