Some people won't go anywhere without their PalmPilot. Consider Jefferson Lilly, a technology investment banker for SG Cowen Securities Corp. in San Francisco, who this past summer took his PalmPilot to the summit of Mount Kilimanjaro.

That may be taking the popular digital organizer to an extreme, but no one can deny that the PalmPilot is a hit - even at 19,340 feet above sea level. Market analysts at Dataquest report that PalmPilots have gobbled up 41% of the entire handheld computer market. According to Palm Computing, makers of the PalmPilot and a subsidiary of 3Com, there are now more than 1 million Piloteers in the United States.

The PalmPilot's wild success has spawned hundreds of accessories, more than a thousand software programs, and a third-generation device, the Palm III. Not surprisingly, Microsoft aims to get a piece of the action by backing a bevy of Pilot imitators, which run on the stripped-down Windows CE 2.0 operating system.

Trying to choose among the dizzying array of add-ons and knockoffs generated by PalmPilot mania is a bedazzling experience. I know, because I spent four weeks testing and rejecting scads of Pilot-related gizmos, until I had rounded up the very smartest applications. I also forayed into the world of palmtops themselves, and tried out all the options confronting shoppers who must decide among older but cheaper PalmPilots, the new Palm III, and the latest Windows CE copycats. In this edition of PowerTools, you'll learn what I learned.

The PalmPilot: Doing More with Less

The PalmPilot's appeal isn't hard to fathom. Unlike souped-up personal digital assistants, the PalmPilot doesn't attempt to do the work of a complete computer. The device simply does what it's supposed to do, and it does it very well: Track appointments and contacts, synchronize them with a desktop computer, and take the occasional note.

The PalmPilot organizers come in three editions: the PalmPilot Personal, the PalmPilot Professional, and the newer Palm III. If you're on a tight budget, check out the PalmPilot Personal ($199) with 512K of memory. PalmComputing has discontinued production of the Personal edition, but some retailers are still carrying it. The machine has all the features of the original models (such as the date book, address book, To Do list, calculator, and memo-pad programs), plus an improved version of the built-in software, dubbed Palm OS 2.0, and "Expense Tracking," a program for recording your expenses. But the Personal edition won't let you email over the Internet.

For the best value, consider the Palm-Pilot Professional ($299). Its improvements over the Personal edition include an Internet email program and more memory (1MB) - enough to store about 10,000 names, dates, and other information. The email program doesn't actually dial into the Internet, but rather it grabs unread mail from your desktop computer's email program.

If you're shopping for your first PalmPilot, spring for the Palm III ($399). While it has the same basic organizer software as the Professional (including a date book, address book, To Do list, memo pad, and pocket email), the Palm III comes with 2 MB of memory, enough for 20,000 names and dates.

Palm Computing has also improved the Palm III's basic operating software (upgraded to Palm OS 3.0) - it's faster, it sports different-sized fonts, and it offers support for beaming capabilities. This last feature means that you can "beam," say, a digital business card to another Palm III user - but you can't do the same with a PC. That's because the Palm's infrared transmission doesn't conform to the PC industry standard known as IrDA (Infrared Device Association).

If you already own a PalmPilot Professional, there's no need to move up to the Palm III. The minor improvements don't justify replacing your existing model. If you're thinking about upgrading, Palm Computing does offer a pop-in hardware upgrade ($130) that gives you the infrared port, the additional memory, and updated software. But I recommend that you stick with your old model until you accidentally sit on it. Better versions will undoubtedly be out by then, for less money.

Coordinates: PalmPilot, Palm Computing Inc./3Com, 800-881-7256, www.palmpilot.com

PalmPilot Copycats - or Killers?

If you launch a winner like the palm-Pilot, you can bet that Microsoft will follow. And follow it has, with a version of its Windows CE 2.0 operating system adapted for limited-function computers that are roughly the size of the PalmPilot.

Microsoft has partnered with hardware companies to launch a bevy of PalmPilot copycats, inelegantly dubbed "Palm-size PCs." They do everything the PalmPilots and Palm IIIs do, plus a little more.