The latest major update for Windows XP was due for release this week, though a last-minute hitch appears to have caused some problems.

XP Service Pack 3 was originally scheduled for download through Microsoft's update service on Tuesday. However, the firm temporarily halted the updates after finding compatibility problems with Microsoft Dynamics RMS. That's a software package that helps small and medium businesses manage their supply chains.

Microsoft is now putting a filter on the download service to identify which computers are running the Dynamics software. They'll then re-release the update to all unaffected computers. There was no official word as to how long it will take to get the filter running, or indeed to solve the compatibility problems.

The problem also affects Vista's Service Pack 1, but it appears that update had already made it onto most Vista machines before Microsoft discovered the issue, so there's little point halting that update process. (Source: news.com)

The big difference is that the Vista update had already reached the point where computers were automatically downloading it. At the moment, the XP update is only downloaded where users specifically request it. The automatic update likely won't take place until mid-June.

XP Service Pack 3 is the biggest update to the operating system for four years. That's when the logically-enough named Service Pack 2 came out; the biggest change then was the addition of Windows Firewall.

As well as collecting together all the minor updates during that time (which some users may have missed or chosen not to install) Service Pack 3 includes new editions of Windows Media Player and Internet Explorer, plus improved security for wireless Internet. (Source: internetnews.com)

Given that XP is set to be withdrawn from sale this summer, it's likely this will be the last major update. Users probably won't notice any major differences once Service Pack 3 is installed; it's Microsoft's equivalent of giving an old car a tune up and polish before trading it in for a new model.