No matter how well designed a piece of software is, or how thoroughly tested it has been prior to its release, there are often problems that only come to light once the likes of you and I start using it on a large scale.

Irritating though it may be to discover glitches in a program you've only just installed, software companies will usually act quickly to counter flaws in their products by releasing freely downloadable updates, or patches. These can be found on the manufacturer's website.

When it comes to the biggest piece of software on your computer, the Windows operating system, things are a little different. Windows is massive, so the scope for imperfections is far greater than it would be in a simpler program.

Bear in mind just how much hard disk space an installation of Windows takes up: around 190Mb for a basic installation of Windows 98SE, 480Mb for Windows Me and a huge 1.5Gb for Windows XP.

Microsoft has also crammed loads of additional software into Windows, such as Outlook, Windows Media Player, Internet Explorer and Windows Messenger, which wouldn't ordinarily count as part of an operating system. This further adds to the amount of software in which flaws may occur.

These flaws are the gaps through which viruses, hackers and other threats crawl onto unpatched machines. Microsoft says that it has always tried to make software easy to use, while some angry users have accused the company of not putting enough emphasis on PC security. Whatever the arguments, the company seems to be taking it a lot more seriously now.

Because many users don't download the constant drip of patches from Microsoft to defend Windows products, the company periodically releases an omnibus edition, known as a service pack, or SP.

SP1 for Windows XP was released about six months after XP made it's debut. Most of the updates in SP1 worked behind the scenes to make your experience of using Windows safer and smoother and did a number of useful things, including adding support for high-quality surround sound audio and USB2 connections.

As the next version of Windows is not due for release until 2007 at the earliest, Microsoft has released a more comprehensive set of updates that includes additional features as well as fixes for software security flaws.

Get a little extra
So what additional bells and whistles will SP2 bring to your PC? The most obvious change to Windows itself is the new Security Center, which takes pride of place in the Control Panel and which you can access in the Start menu.

Software bugs that affect the performance of Windows and the applications bundled with it are a serious issue, but security flaws are more of a worry. Many virus writers set out with the specific intention of exposing and exploiting flaws in Windows.

There are people out there who will be only too happy to use a weakness in the operating system to try to gain access to an unprotected PC.

The new Security Center draws together the much-improved Windows Firewall, the settings for Automatic Updates for Windows and software that monitors the state of your antivirus application. If you don't have your firewall and antivirus software enabled, SP2 will nag you until you give in and take the proper steps.

There are also changes to the Windows Update feature, which means if your internet connection fails while you're downloading an update from the Microsoft site - including SP2 itself - it will resume where it left off when you get back online. This also means that you don't have to download SP2 all in one go.

There are additional tools for wireless security and a new wizard to simplify the process of setting up a wireless network. Add in a pop-up blocker for Internet Explorer and that's already a decent list of extra features.

Installing the service pack
So how can you get your hands on SP2? As with most Windows patches, it is downloadable from the usual Windows Update site.

If you use a dial-up connection to get online, you should be aware that at a minimum size of 90Mb, SP2 could take up to 4 hours and 21 minutes to download. You might want to try to download the patch off-peak when call charges are cheaper.

Incidentally, that 90Mb figure assumes that you have already downloaded and installed SP1. If you haven't, you're looking at a 110Mb download, which will add around another hour to that download time.

If you pay by the minute for internet access, this is hardly going to act as an incentive to keep Windows up to date, but there is an alternative. SP2 will be made available as a free CD, which dial-up users can order online on the Windows update site. Microsoft will even pick up the tab for packing and postage.

Before you even think about installing SP2 on your PC, though, it's a good idea to back up all the data on your computer, ideally onto a CD or DVD. You can use software such as Power Quest's Drive Image to make a copy of the contents of your PC's hard disk, which costs around £40.

Also consider using System Restore, which will take a snap shot of the PC's system files and some program files so you can restore them to a working state should anything go wrong. It only takes a few minutes and if you hope for the best and plan for the worst you should avoid trouble.

Windows will make a copy of certain system files automatically before it starts to install SP2, but it's worth taking advantage of any precautionary tools at your disposal to ensure you don't lose vital data.

Starting the actual download process is a simple matter of clicking on the Scan for Updates link on the Windows Update site and then following the instructions that appear on the screen.

Once SP2 is fully downloaded and ready for installation, the SP2 Setup Wizard will appear on screen and guide you through the process of installing the patch. You should close any software running on the PC that may affect the installation process when prompted to do so.

Good housekeeping
Updating your version of Windows XP with SP2 may seem like a hassle, particularly if you're a dial-up user and are faced with either the prospect of a lengthy download process or having to order a CD and waiting for it to arrive.

While the extra features and wizards included in the patch may sweeten the pill, it's the security fixes that make this patch an essential update for any PC running Windows XP.

You may have to devote a few hours to the task in hand, but we can't stress enough how important good housekeeping is when it comes to keeping your software up to date and protecting your PC.