The Portable Media Center -- a new, Microsoft-conceived handheld device that presents video and photos as well as music -- would be a decent idea if there weren't such a thing as lampposts. Or street signs. Or trees. Or other cars.

All those obstacles explain why no sane person tries to walk, run or drive while watching video, even as millions do partake in those activities with music playing.

A Portable Media Center's ability to display photos and play back recorded TV programs, digital video clips and downloaded movies is supposed to set it ahead of mere digital-music players, but there just aren't that many places where you can make use of it. Everywhere else, a Portable Media Center turns into the world's heaviest, biggest, costliest MP3 player.

One such device is available now -- Creative Labs' $500 Zen, which I've been toting around for a few weeks. It resembles an overweight Game Boy more than anything, with a color display, 43/4 inches across, flanked by two sets of controller pads (twice what an iPod needs for same basic functions). An onscreen interface mirrors the clean, refined front end of Microsoft's Media Center edition of Windows XP; inside, a hard drive offers about 18.5 gigabytes of storage.

The Zen is a brick of a device, just over an inch thick and slightly more than three-quarters of a pound. Not all Portable Media Centers are as hefty; Samsung's thinner, lighter YH-999, for instance, is more like a tile or a paving stone.

All Portable Media Centers require Windows XP, Windows Media Player 10 and a USB 2.0 port (you can use one with a slower USB 1.1 port, but it will take hours to copy files that way). When you first connect one to your computer, Windows Media Player will offer to copy your music, photo and video collections to the Media Center's hard drive, then keep everything in sync between that device and the PC.

The sync process, however, ran aground on one of two test systems, when Windows Media Player declined to transfer some songs bought from the Napster site, offering only this explanation: "Windows Media Player has encountered an unknown error."

Portable Media Centers play regular MP3 and Windows Media Audio files, as well as songs purchased off stores that use Microsoft's Windows Media standard, such as Napster and Microsoft's own MSN Music -- but not files downloaded from Apple's iTunes store. They can also play songs rented from Napster's upcoming Napster to Go service; this new option lets users pay a flat monthly fee to download all the music files they want (in return, all these files stop working if you cancel your subscription).

As a digital-music player, the Zen's sole advantage is battery life, estimated by Creative at 22 hours. It's just too big to run with or even to stash in a pocket. Every time I took it on my commute, I spotted other passengers listening to their iPods and couldn't help imagining what they'd think of anybody lugging around such a chunky gadget: "loser."

The Zen came down with another form of sync sickness when I tried copying my digital pictures to the device. On one computer, Windows Media Player synced a handful of graphics from a help file in addition to the photos in the My Pictures directory; on the other, this software went completely off the deep end and synchronized hundreds of unwanted pictures, including cached Web-page files and desktop backgrounds.

Once I'd cleaned those extras off the device, I found that I couldn't display the pictures in each folder in the most logical order -- by the dates and times they were taken. Instead, the Zen sorted them by file name, a real pain when you have 200 pictures whose names all begin "image001." There's also no way to zoom in on a photo to see more detail.

The Zen's biggest flaw as a digital photo album, however, is its day-to-day irrelevance. The big reason to carry entire libraries of digital photos around is to share them with other people, and for that purpose a 10-cent recordable CD will suffice.

The Portable Media Center concept faces a different problem when it comes to video use. Most computers can't record TV programs to their hard drives in the first place, while the supply of legal TV or video downloads is also near-nonexistent. Only one site, CinemaNow, offers movies that can be transferred to a Portable Media Center -- a scant 167 films, mostly B-movie rejects.

Nor can you simply plug a Portable Media Center into a cable or satellite box to record directly from that feed -- the only way to load video is from your computer.

You can, of course, grab plenty of video off file-sharing networks. But this may not work smoothly either; a movie download in the popular DivX format took more than two hours to convert to a Portable Media Center-ready form on a relatively new laptop, then played on the Zen jerkily and in the wrong aspect ratio (meaning everybody on the screen looked freakishly skinny).

The Zen and other Portable Media Centers can be plugged into TVs, but on a larger screen the defects of these compressed video files -- a blurry, blotchy, low-resolution picture -- were embarrassingly obvious.

I got about seven hours of battery life while playing video on the Zen, more than enough for a domestic flight. I could also see a device like this getting regular use among workers with lengthy train commutes.

But a portable DVD player will save you a few hundred dollars and provide a much better selection of movies to watch.

The toughest competition for the Portable Media Center, however, is not even that but the latest crop of Palm and Pocket PC handhelds, all of which feature memory-card slots (a one-gigabyte card goes for under $100 these days) and screens almost as big as the Zen's. They require a little more tinkering and can't store nearly as many music, photo and video files, but they also do useful tasks such as remembering your schedule and address book. And they're a lot less likely to wind up in the graveyard of Gadgets People Don't Need.

Living with technology, or trying to? E-mail Rob Pegoraro at rob@twp.com.

The Zen, by Creative Labs, weighs in at a little more than three-quarters of a pound.