A personal computer’s operating system is its brains. It tells your programs how to interact with your hardware, transmitting your intentions into words, calculations, photos, or any of the other tasks PCs handle.

Whenever an operating system is upgraded, it’s big news. The release of Windows Vista, the newest version of the world’s most popular personal computer operating system, is huge. It forces you to ask yourself a question: What should I do?

The short answer for most is to watch and wait. If you already knew this, you can stop reading now. If you’re curious about some of the ins and outs, read on.

I’ve read everything I can about Microsoft’s latest and greatest. I’ve talked to some key people and have run Vista on one of the machines here.

PC Magazine , the leading computer monthly magazine, is gung-ho, as you might expect. Geeks love new tools. In a phone interview, executive editor Jeremy Kaplan told me that the magazine staffers installed Vista onto about 5 dozen computers and put it through hundreds of hours of testing.

“There aren’t any glaring problems that would cause us to advise people to wait to upgrade,” said Kaplan. The upgrade process itself, he said, is “painless.”

Painless can mean different things to different people and different computers. The upgrade, for one thing, costs anywhere from $99 for the no-frills, so-what “Home Basic” upgrade to $259 for the complete “Ultimate” upgrade.

But to take advantage of all the features in the Ultimate upgrade, you need a new and powerful computer. Microsoft provides a “Vista Upgrade Advisor” (www.windowsvista.com/upgrade) that you can download and run to help determine which version of Vista is right for you. But Microsoft’s minimum requirements are a bit minimalist, and for best results, your machine’s processing power, memory, hard disk, and video card should be a bit beefier than indicated.

One of Vista’s key selling propositions is improved security. Compared with Windows XP, Windows Vista does a better job of helping to prevent hostile programs and Web sites from attacking your PC. But if you’re already using a security suite such as Norton Internet Security or McAfee Total Protection (and you should be), you’re already protected.

The most noticeable change in Vista is its interface. If you have even a little geek in you, you’ll no doubt find it cool. The windows are transparent and animated, and they swoosh into place, provided you have the right hardware.

The interface also provides more function along with form. Using Alt-Tab to switch among open programs displays a three-dimensional thumbnail stack so you know exactly which program you’re going to. Its new search technology not only makes it quick to find files you may have saved to the wrong folder, it also makes it quick to start programs without digging through Start Menu folders.

Vista has a ton of other built-in features, including the performance-boosting preloading of programs, an Internet weather forecasting module, an image-editing and slide-show utility, a movie maker, a parental control tool for protecting kids, and better tools for networks and notebooks.

PC Magazine contends that Vista is reliable, with much credibility. But others advise users to wait and see, which has long been the most prudent approach to major upgrades. The first service pack, or bundle of bug fixes and product enhancements, will likely be out sometime during late summer or early fall.

David A. Milman, founder and CEO of RESCUECOM, a national computer repair outfit that bails people out of PC trouble, advises individuals and businesses not to switch to Vista just yet. “We’d hate some minor glitch to result in major headaches for our customers or anyone else. We suggest waiting six months.”

In short, if you’re an “early adapter,” and you know enough to know what that means, dive right in. The water’s fine. If you’re a typical home or small business user, weigh your hardware horsepower and the extra functionality that Vista provides, and consider upgrading when the service pack comes out.

If you’re responsible for a business with 500 or more computer users, you don’t need me to tell you that any move to Vista will require testing and more testing to make sure it works with your existing programs and security system.

One last option, which I suspect will be the default for the vast majority of people, is to keep your current set-up until it’s time to buy a new PC. It will come pre-loaded with Vista, and you’ll know it has everything needed to run everything Vista has.