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When Microsoft released Windows XP in October of 2001, the software got upbeat reviews and sold briskly. But I doubt if even XP's biggest boosters would have predicted just how long-running a hit it would be. Nine years later, it's still the the world's favorite operating system.

Two words explain XP's uncommonly long reign: Windows Vista. The much-hyped 2007 Windows upgrade turned out to be notoriously glitchy (especially at first) and short on substance. Some PC users tried Vista and loathed it; others simply chose to avoid it. Either way, XP got a new lease on life.

And then Windows 7 arrived last October. For the millions of PC users who chose to skip Vista, 7 is the upgrade to XP. And it's a nifty one, retaining what was good about Vista -- such as the ability to instantly search your entire hard drive -- while fixing every major problem. Features for juggling multiple applications are greatly improved, and annoyances such as pop-up messages are much reduced. Overall, Windows 7 is just plain pleasant in a way that even XP isn't.

Even so, when I reviewed Windows 7 back in October, I told would-be upgraders that there was no shame in waiting a bit just to make sure that the early adopters who installed it on day one didn't discover any nasty surprises. For the most part, they didn't -- and the vast majority of those who participated in a survey I conducted raved about the software.

So today my advice is simple: If you're buying a new PC, get Windows 7. And my recommendation to XP users who aren't ready to get a new machine is only a little more complicated: Unless you're really resistant to change or have a really old PC, spending $120 on Windows 7 Home Premium edition is a great way to get more out of your computer.

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But before you take the Win 7 plunge, do this:

Make sure your PC is up to the task. Most computers sold in the past few years should do a decent job of running Windows 7. But it's still wise to run Microsoft's Windows 7 Upgrade Advisor, which will do a quick system check and provide customized upgrade advice. (One tip: If your PC doesn't already have 2GB of RAM, get it.)

Back up. I've heard very few horror stories of Windows 7 upgrades gone awry, but you don't want to be the exception that proves the rule. Before you begin the process, make sure that you've backed up your data to an external hard drive or an online service such as Mozy -- especially irreplaceable items such as family photos and videos.

Take your time. Unfortunately, Microsoft doesn't give you any way to install Windows 7 over XP, retaining existing programs and settings. You need to install a fresh copy of the operating system, reinstall your favorite software, set up peripherals such as your printer, and generally recreate your environment the way you like it. Consequently, it's best to do the job when you're not in a huge hurry. (I've been known to upgrade Windows on otherwise lazy weekends.)

What if you're still not convinced that it's time to give up XP? Fret not -- I'm done trying to convince you otherwise. In fact, I'll provide some tips for you, too:

Stay up to date. Let's face it, XP is inherently antiquated. But it's an antiquated operating system that's still evolving, especially when security vulnerabilities are discovered. Use Microsoft's Windows Update service to verify that you're running Windows XP Service Pack 3, the most recent major update -- and that you're getting new security patches as they come out.

Get a modern browser. Don't use Internet Explorer 6, XP's default browser -- it has too many security holes and is too lacking in essential conveniences, such as tabbed browsing. At the very least, upgrade to Internet Explorer 8, the current version. Better yet, try one of the two Windows browsers I recommend most often these days: Firefox and Google Chrome.

Prepare for the inevitable. Unless you have no interest whatsoever in new software, hardware or services, you will say goodbye to Windows XP at some point. Microsoft has repeatedly bowed to reality, allowing manufacturers to put XP inside the boxes of even Windows 7 PCs as a "downgrade" option. But XP's time is almost over, and there's going to be more and more interesting stuff that won't work with it, such as Microsoft's own upcoming Internet Explorer 9, which will support Vista and 7 only.

So feel free to hold onto XP if you choose. Just know when to say when -- and understand that the day is coming soon.

Harry McCracken blogs at Technologizer, his site about personal technology. He's also the former editor in chief of PC World. Follow him on Twitter as @harrymccracken.