Following the release candidate preview for Windows Vista Service Pack 1 which was made available to testers earlier this month, Microsoft has begun rolling out an updated test version of Windows XP Service Pack 3 to about 15,000 beta testers.

A public test version of the service pack, which will be the last major update to the aging operating system, is expected “at a later date” followed by its final release sometime in the first half of 2008. Microsoft has said little about what will be in Windows XP SP3, leading to much speculation over the timing and features of the release, which will likely be a roll-up of existing hotfixes.

The final release of the first service pack for Windows Vista is also due out in the first half of next year, and is likely to be released ahead of XP SP3 in a bid to encourage XP users to upgrade to Vista.