If you’re the adventurous type, or like to be the first on the block with new technology, then you might want to check out the new public test versions—"release candidates" in geek speak—of Windows Vista and Windows XP.

Release candidates are typically pretty close to finished. But they can still contain glitches (which is why companies like Microsoft allow the public to play with pre-release software in the first place: to help ferret out and squash any stubborn remaining bugs). I wouldn’t recommend installing either of these updates on any computer with data you can’t afford to lose. But if you have a spare PC and want to glimpse the future, here’s what’s available:

On Wednesday Microsoft unveiled the pre-release version of Windows XP Service Pack 3 (SP3). The 336 megabyte download is the company’s last planned comprehensive update to its venerable operating system. But before XP fans get their hopes up, know that this isn’t the same goodie-packed gift of service packs past. SP3 is primarily an anthology of security patches and miscellaneous tweaks that have trickled out of Redmond since Service Pack 2 went public in 2004. If you’ve been diligent about keeping your computer up to date, then chances are you already have much of what SP3 has to offer. There is a smattering of new features, but these frankly are aimed at corporate technology managers, not folks at home. You can read more about what’s in SP3 here.  But as Windows guru Paul Thurrott noted, "This update certainly brought back some nostalgic memories. But seriously, folks: It’s time to walk away." Walk away to Windows Vista, he means. According to Information Week, the final version of the SP3 is expected to ship early next year.

The first major Vista update, on the other hand, is definitely something to get psyched about. Earlier this month Microsoft made the pre-release version of Windows Vista Service Pack 1 (SP1) publicly available to try out. I know opinions on Vista differ—and that’s putting it politely. But I think naysayers and holdouts will begin to soften once they get their hands on the new service pack. Like many employees, I’ve been playing with pre-release versions of SP1 for months (part of a tradition lovingly known among Microsofties as "dogfooding"). While the new update doesn’t have a ton of flashy eye-candy, it’s made lots of improvements under Vista’s hood. My PC definitely has more pep and behaves less quirkily since I installed it. If you’ve got time to kill over the holidays, you can kick back with the full list of what’s in SP1. Todd Bishop at the Seattle PI offers a shorter, plain English run down on his blog. The final version of SP1 is expected in the first quarter of 2008.

<Michael Stroh>