The real question is, what isn't new?

Windows Vista is a huge overhaul. Both the guts and the window dressing have been completely renovated. Here's a top-level executive summary.

Security

For 5 years, through multiple restarts and reshufflings of the Vista project, Microsoft became obsessed with making Windows more secureand there are few who'd say that its obsession was misplaced.

You could fill several books with nothing but information about the security featuresa lot of them are so technical, they'd make your eyes glaze overbut here's a sampling.

• User Account Control may look to you like a completely unnecessary annoyance: a dialog box that pops up whenever you try to install a program or adjust a PC-wide setting, requesting that you type your password. Over, and over, and over.

  In fact, UAC is one of Vista's most important new protection features, modeled on something similar in Mac OS X and Unix. It means that viruses can no longer make changes to your system without your knowing about it. You'll see one of these dialog boxes, and if you aren't the one trying to make the change, you'll click Cancel instead of Continue.

• The Security Center offers one-stop shopping for several important security features: the firewall (protects your PC from incoming signals from hackers), Automatic Updates (bug fixes and security patches beamed to you from Microsoft), virus and spyware protection, Internet security settings, and User Account Control.

• Windows Defender is a new program that protects your PC from spyware (downloads from the Internet that, unbeknownst to you, send information back to their creators or hijack your Web browser).

• Protected Mode is a new feature of Internet Explorer that keeps hackers from attacking it.

• A phishing filter alerts you when you're about to visit a fake bank or eBay Web page to "update your account settings." In fact, you're probably being scammed. You've been sent a bogus alert email that, in fact, is a trap set by scammers hoping to steal your account and credit-card information.

• Service Hardening prevents invisible background programs from tampering with the system files, the Registry, or the network.

• Corporate features let network administrators exert a lot more control over what the worker bees are doing. Your company's network geeks, for example, can institute a group policy (a corporate network "rule") that bans the use of USB flash drives, to prevent viruses from coming in or important documents from going out. They can also prevent any "unsafe" PC (one whose Microsoft patches and virus program aren't up to date) from even connecting to the network.

• Parental Controls lets you, the wise parent, restrict children's use of the PC. You can dictate what Web sites they can visit, which people they correspond with online, and even what times of day they can use the machine.

• BitLocker Drive Encryption encrypts your entire hard drive, so that even if determined hackers steal your laptop and extract the drive, they'll get no useful information off it.

• A new backup program offers two modes: backup by file type (all your photos, music, and Office files, for example) or complete PC backup (all your programs, system files, the works).

  And remember System Restore, the life-saving troubleshooting tool that lets you rewind your PC to a time when it was working properly? A sister feature, Shadow Copy, offers the same safety net to individual documents.

• Address-space randomization moves system files around in memory randomly. The idea here is to make it extremely difficult to write a virus that will work the same way on every PC.

A Cosmetic Overhaul

As you've probably discovered already, Windows Vista looks much more modern and colorful (and, frankly, Mac-like) than its cosmetically challenged predecessors. Thanks to a new design scheme called Aero, Window edges are translucent; menus and windows fade away when closed; the taskbar shows actual thumbnail images of the open documents, not just their names; all the icons have been redesigned with a clean, 3-D look and greater resolution; and so on.

The Start menu is a better-organized, two-column affair; that awful XP business of superimposing the All Programs menu on top of the two other columns is long gone.

By the way, if you don't care for the Vista cosmetic changes, you can turn them off selectively, which makes your desktop look and work just as it did in previous versions of Windows. You can also turn off the various animations, drop shadows, and other special effects for a measurable speed boost on slower PCs (see page 612).

Merged OSes

There are no longer separate Windows Media Center and Tablet PC Editions; these features are now built right into certain versions of Vista.

New Programs and Features

Lots of new or upgraded software programs come with Vista (or at least some editions of it). For example;

• Photo Gallery. A tidy little digital shoebox, suitable for touching up, organizing, and sharing your digital photos.

• Instant Search. With one keystroke, you open the Start menu's new Search box. It searches your entire PC for the search phrase you typeeven inside files that have different names. It's the ultimate efficiency boosterand, by the way, a fantastic way to open programs without ever taking your hands off the keyboard.

• Windows Calendar. A very simple calendar for planning your life.

• Windows Mail. OK, it's really just Outlook Express with a new name, but it does have a spam filter now.

• Windows DVD Maker. Burns video DVDs, complete with a scene menu and background music.

• Windows Meeting Space. A Vista-only replacement for NetMeeting. It lets you and your colleagues see each other's screens and pass around notes or documents across the network or the Internet.

• Snipping Tool lets you capture rectangular or irregular patches of the screen as graphics, for use in illustrating computer books.

• Windows Fax and Scan offers one-stop shopping for scanning, and for sending and receiving faxes.

• Internet Explorer 7 has been beefed up. It now has tabbed browsing, RSS news feeds, and about 65,000 new security features.

• Windows Media Player 11 has yet another new look. It can share your music and photos across the network with another Vista PC (or an XBox 360), too.

• Speech Recognition isn't as accurate as, say, Dragon NaturallySpeaking. But it's light-years better than Windows' old speech-recognition feature. If you have a headset, you should try it out; you can dictate email and documents, and even control Windows itself, all by voice.

• Laptop goodies including folder synchronization with another computer, more powerful battery-control settings, and a central Mobility Center that governs all laptop features in one place. The ingenious Presentation Mode prevents dialog boxes, screen savers, alerts, or sounds from going off when you're in the middle of a presentation.

• SuperFetch speeds up your PC by analyzing when you tend to use certain programs, so they'll be ready and waiting when you are. ReadyBoost lets you use the RAM on a flash drive as extra memory for greater speed. (Cool!)

• The Sidebar. This feature offers a floating panel filled with tiny, single-purpose programs called gadgets: a stock ticker, weather reporter, address book lookup, and so on.

New Explorer Window Features

At the desktop, the Explorer windows, where you view the icons of your files and programs, are bristling with new features.

• New panes. Explorer windows can now have information panels and controls on all four edges, including the new Navigation pane (left); task toolbar (top); Preview pane (right); and Details pane (bottom). You can edit those details (that is, properties) right in the window, even adding tags (keywords) for fast, easy rounding-up later.

• Stacking, filtering, and grouping. Every Explorer window offers three new methods of slicing, dicing, finding, and categorizing the files inside.

• Document preview. Now you can see what's in a document without having to open it first. Its icon actually is the first page of what's inside. That's an especially handy feature when it comes to photos. You can also play movies and music files right at the desktop, without having to fire up a program first.

• Address bar. The new Address bar, which displays the path you've taken to burrow into the folder you're now inspecting, is loaded with doodads and clickable spots that make navigation far easier.

Version Hell

You thought Windows XP was bad, with its two different versions (Home and Pro)?

Windows Vista comes in five different versions: Home Basic, Home Premium, Business, Enterprise, and Ultimate. And that's not even counting the Starter edition, sold exclusively in poor countries outside North America, or the two "N" versions (like Home Basic N), which are sold in Europe to comply with a different set of antitrust laws.

Microsoft says that each version is perfectly attuned to a different kind of customer, as though each edition had been somehow conceived differently. In fact, though, the main thing that distinguishes the editions is the suite of programs that comes with each one.