It’s an idea whose idea has come. Again.

Back in the dotcom day, IBM and several other major players hawked the “thin client.” Their theory was that you could do all your daily work on a Web server, via a customized browser running on your specialized network appliance or PC.

This potential breakthrough in cost and ease of management broke down in two big ways. Users didn’t think the Web versions of their familiar desktop applications were powerful enough, and they gave up altogether when connections to the server were broken or simply too slow.

But other Web-based applications continued to flourish. IBM kept puttering away on server-driven applications for general office tasks. And last week Big Blue raised its game with the introduction of its ambitious Workplace 2.0: a “middleware” application infrastructure designed to let organizations deliver and manage programs that run on PCs, handhelds, and smart phones but that are entirely controlled by servers.

The biggest twist in Workplace 2.0 is its new Workplace Client Technology, which IBM says overcomes the barriers of functionality and imperfect connections that are faced by server-driven clients. IBM describes this as a “rich” rather than a thin client.

As with other existing Web clients, Workplace Client programs can be delivered, managed, and updated directly from the server, thus slashing IT management costs. For instance, an entire organization can be upgraded to the next release of a word processor without having to monkey with any desktop machines. Workplace also boosts security, running only applications that have been authorized by the customer organization.

But IBM says Workplace Client will provide full-featured interfaces and powerful tools like those of standard PC applications, rather than the simple browser-based interfaces and constrained capabilities of thin clients. Each organization can download just the components a given user needs, rather than take the one-size-fits-all approach exemplified by Microsoft Office. (Does everyone really need, say, Excel 2003’s continuous probability distribution functions?)

Workplace Client packages also will run perfectly well when disconnected from the server, saving their content in a local encrypted data store that synchronizes with the server when connections resume. This turns a thin-client liability into a plus, since files are both automatically backed up on the server and more easily shared with co-workers, says Mark Levitt, vice president for collaborative computing research at IDC.

The first two Workplace Client packages, Lotus Workplace Documents and Lotus Workplace Messaging, are scheduled to arrive next month. These feature many of the same tools as Microsoft Office (Workplace Documents, for instance, bundles word processor, spreadsheet, presentation, and other components).  The pricing is aggressive: $24 for the Workplace client plus $2 per user per month for each Lotus Workplace application. That’s a fraction of what customers often pay for Office.

IBM doesn’t expect to write most Workplace applications, though. Workplace is an open platform based on industry standards, and major vendors such as Adobe and PeopleSoft have signed up to offer their own versions. Workplace Client supports Windows and Linux PCs, with Macs to come, and there’s a version for a wide range of mobile devices besides PCs.

Big Blue claims more than 110 million users of its existing Workplace offerings, which include the Lotus Notes/Domino collaboration and WebSphere application platforms. The Workplace 2.0 rollout has drawn a great deal of interest, especially for the hefty cost savings it promises. Support for applications that run across a broad range of client computing devices also appeals; “the idea of a single infrastructure sounds good,” says IDC’s Levitt. “It’s an environment that can coexist very well with Windows or in some accounts push out Windows.”

Don’t expect any quick stampede away from Office, though, says Gordon Haff, senior analyst at Illuminata in Nashua, NH. “It’s very difficult to get people to change their models of doing things,” he says.

Haff maintains that IBM’s server-driven rich client can’t quite deliver the best of both traditional thin Web clients and PCs. While existing thin clients are less functional than rich clients, they also are easier to control. And that pays off not just in operating costs but in security. “If you’re still based on a Microsoft desktop, you still get all the security aspects of a Windows machine,” Haff says. “There’s no doubt that the thin client is in general better for security,” he argues. “Simplicity and security go hand in hand.”

The clearest path toward securing these rich clients may be one that IBM is reluctant to take. “One obvious evolution is to an appliance-like environment that’s more locked down,” Haff says. He points out, however, that IBM and other companies dabbled unsuccessfully in such products back in the late 1990s and may be leery about trying again,

If application vendors do buy into Workplace, we just might see dedicated Workplace hardware on both desktop and handheld computers. Historically, PCs have steamrolled over such specialized hardware for office tasks, winning via manufacturing volume, and sheer programming flexibility. But the ability to run any PC application that comes along may not be so important in an era when innovation has moved to the Web. Client hardware costs are dwarfed by operating costs. And corporations are desperate to grab any measure that could improve security in an ever-more-insecure online world.