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Whether you consider Microsoft friend or foe, it's hard to deny that Windows 2000 Professional is the most stable, capable version of Windows yet. If you've come up against the flaws and limitations in Windows 95 or 98--and you aren't about to jump on the Linux bandwagon--you probably want Windows 2000 on your business PC.

But wait a minute. Sure, compared with Windows NT 4.0, Windows 2000 offers vastly improved hardware and software compatibility, but it's still not as easy as Windows 98. Hasty upgraders may find themselves muttering expletives when key programs, devices, and data go AWOL. The trick to a successful upgrade is to do your homework in advance by researching your system's compatibility. And leave yourself an escape route back to Windows 9x or NT, in case the Windows 2000 honeymoon turns prematurely sour.

To help you avoid trouble, we tested late beta versions (Release Candidates 2 and 3) of Windows 2000 Professional--and late in our testing process we received the final software version from Microsoft. We attempted upgrades on 24 computer systems (ranging from a Pentium-133­based machine to Pentium III-550­based units), and we tested 29 peripherals and 16 applications for compatibility with Windows 2000. We started upgrades from Windows 95, Windows 98, Windows 98 Second Edition, and Windows NT. In some cases, we installed Windows 2000 over older versions of Windows, and in other cases, alongside them.

The results revealed a brutal truth: Depending on your hardware and applications, a Windows 2000 upgrade can be either a breeze or a nightmare. For the smoothest upgrade possible, read our suggestions below before you even buy the software.