Microsoft has finally released its SP2 update for Windows XP, whose hype has only been matched by its constant delays in being released.

However, things are still far from running smoothly with IBM advising its employees not to install it because of compatibility issues. Microsoft has previously warned that due to the large number of deep changes that SP2 makes, that it may conflict with other software.Some users have already reported problems. Last week, the software giant even admitted its own CRM software was adversely affected.

In a note headlined "To patch - or not to patch" posted on IBM's corporate intranet, employees were told not to download SP2. "While this patch may be good news for other Microsoft Windows XP owners, IBM is directing XP users not to install SP2," it stated.

"IBM's large number of Web applications will need to be tested and some modified to work correctly with SP2. Currently, some high profile, business-critical applications are also known to conflict with SP2," IBM told employees. "When the current issues and concerns have been addressed, IBM will deploy a customised version of SP2."

The note came the same day that Microsoft started delivering SP2. The update will be available soon through downloads, retail distribution and free CDs, as well as on new PCs. A network installation package will be available for enterprise users.

The easiest way for users to get SP2 is to turn on the Automatic Update feature in Windows XP, Microsoft has said. It will start pushing out SP2 "in the coming days", reports Carol Sliwa of Computerworld.

At about 265MB, SP2 is not small. But Microsoft said it expects the average file size to be much smaller because of the "smart download" technology that installs only what the user needs. That means users who already have SP1 and have regularly updated their computers with patches shouldn't need to worry about the full 265MB.

The average download for Windows XP Professional is expected to be about 100MB, according to Microsoft. The average download for customers with XP Home Edition is estimated at 80MB. Customers who need SP1 can expect the download to be 20MB larger, Microsoft said.

Download speed will depend on a user's Internet usage, location, language and the level of Internet demand for SP2. The company said it expects to distribute SP2 to about 100 million PCs through Automatic Update, where SP2 will be downloaded gradually in the background whenever a user is online.

Users who prefer CDs can order them from Microsoft free of charge. New PCs preloaded with SP2 are expected to arrive in the retail channel during September and October. Microsoft said it is distributing SP2 to corporate users either through direct communications or its traditional channels. IT managers can find the updates at the Download Center on Microsoft's website, MSDN, TechNet and volume licensing CDs.

Because of the broad changes, analysts have compared the XP service pack to a Windows upgrade instead of a simple update. Business users typically take much longer to install a new version of Windows than a service pack because of compatibility testing.

Nevertheless, Microsoft urges all users to install SP2 as soon as they can. Business users obviously need to test, but Microsoft can't be blamed if users are now unpleasantly surprised by SP2, said Michael Cherry, a lead analyst at Directions on Microsoft. "Microsoft has been more than forthcoming about the number of changes in this service pack and making it available for testing," Cherry said. "I would say to IT departments that they want to get their testing done quickly because there are significant improvements in this service pack and I am not sure you would want to forego those."

A first beta of Windows XP SP2 was released in December, followed by Release Candidate 1 in March and a second release candidate in June. Hundreds of thousands of developers and IT professionals have already tried out the software. The service pack represents one of Microsoft's most broadly tested products to date, the company has said.