(FORTUNE Magazine) – I have a vision! Unfortunately, my vision may depend on Microsoft. So I'm not quite sure that we're going to get what I want.

Here's my vision: In the future we will have an integrated set of personal devices, each with its own purpose, but all working together. The set will include four devices: a mobile telephone (just one), a personal information device (now known as a PDA), a digital tablet (for playing rich media), and a desktop computer (the gateway to the Net and the controller for the other devices). We already have the phone, PDA, and computer. So we just need the digital tablet to fill out the set. Unfortunately, making the vision a reality requires a lot more than just that one device.

We need, for instance, a ubiquitous broadband network so that we can create, acquire, and share rich media on demand--music, movies, photographs. Right now, about seven or eight million Americans have a faster network, like DSL or cable, plugged into their houses. But even that isn't fast enough to let them easily move around files of 40, 50, or even more megabytes--so we need an even faster network.

We also need a speedy, distributed network inside the house to pick up data from the outside for distribution to the devices in the house--phone, PDA, tablet, even the stereo and television. Far fewer than seven million Americans have equipped their homes with Ethernet wiring or wireless networks. But such networks don't yet integrate the phone, PDA, or entertainment devices. And, frankly, the only people who can install and maintain and work with these networks are rocket scientists, not normal people.

We also need a way for these devices to talk to one another and cooperate. Chipmakers are beginning to make what are called Bluetooth chips, which will--in theory--let devices talk to one another when they are close by, so a cell phone could synchronize its phone numbers with those in a PDA or a computer. But theory falls far short of reality. Bluetooth, for instance, doesn't define how a device should decide whether the phone number in your PDA, your phone, or your computer is the most recent. Failing to deal with those kinds of details can kill a good theory.

And we also need, finally, that digital tablet. We need a tablet for all the rich media that don't look good on the other devices. Photographs are great on big computer displays, but you want to share photographs with people in small groups, and lugging around a computer to do that doesn't make sense. Snapshots might work on a PDA, but magazine-style page layouts and product catalogs won't. That is why we need a cool display device.

Microsoft wants to make a really cool digital tablet. Bill Gates said so in his keynote speech at Comdex in November. And the New York Times lavished a big spread on the guy at Microsoft, Dick Brass, whose personal mission is to make said digital tablet. I wish them all the luck in the world. I'm serious. I want a digital tablet myself. Several of my portfolio companies could profit handsomely if people had a way to play their media files on a digital tablet. So not only do I want one for myself, but I stand to make money if a digital tablet gets made.

But I'd never expect any of my portfolio companies to actually make a digital tablet. The damned things are uneconomical. A lightweight, two-inch-thick tablet that has a great screen, enough storage for several movies, fast networking, and long battery life can't be made for less than $1,500 a pop--before adding any software. So how in the world is a manufacturer--let alone a distributor or retailer--supposed to make a profit?

And there's another reason I don't have much faith in Microsoft's ability to design the tablet. In that New York Times article, one pundit was quoted as saying, "The problem with this is that it's still Windows. It's like trying to put wings on a pig; you cannot mutate Windows to give a satisfactory experience in handhelds or tablets."

I know what he means. My new laptop runs Windows 2000. I've only had it for a couple of days, and it seems to work okay. Except that it doesn't. I've had to reinstall a bunch of software. Microsoft Outlook seems confused about where it is on the hard drive, and it's going to take our tech staff a couple of days to help it get unconfused. This laptop is indeed a pig: functional, but in a fat and sloppy way. It's not growing wings anytime soon.

The problem is that Microsoft is a software company. At least, that's what they told the Justice Department. But now they are making a TV set-top box: UltimateTV is due to replace WebTV later this year. And a game machine: Xbox is due next fall. And a tablet computer, due in the next two years, according to Bill.

So let me get this straight: Windows 2000 runs okay after, what, over a decade of Windows? If it takes that long for Microsoft to get its basic product to work decently--forget about its being intuitive or well integrated with other products from the same company--then how long is it going to take the company to get this hardware stuff straight? Can you see why I'm having trouble with my vision?

STEWART ALSOP is a partner with New Enterprise Associates, a venture capital firm. Except as noted, neither he nor his partnership has a financial interest in the companies mentioned. He can be reached at alsop_infotech@fortunemail.com. His column can be bookmarked online at www.fortune.com/technology/alsop.