Longtime rivals Microsoft and Sun Microsystems have made a "180-degree U-turn" in their relationship since signing a legal and technical truce in April, Sun's chief technology officer said Wednesday, and plan to disclose early next year their progress on some customers' No. 1 complaint about the companies: that it's too hard to make their software work together.

During a conference call with reporters, Sun chief technology officer Greg Papadopoulos and two Microsoft executives said the companies' top executives and engineers have been meeting with one another--and their customers--to develop a technical framework for the next decade. Their goal is to make signing on to corporate computer networks, working with 64-bit computers, developing 3-D graphics, and running Java software less of a headache for businesses owning products from both companies.

"Nine months ago, we were slashing each other's tires," Papadopoulos said. In early April, Microsoft paid Sun $1.95 billion in a deal that settled outstanding litigation between the companies about the Java programming language and other issues, and established a plan for resolving technical differences between the companies' products, among the most widely used in IT. Executives from Microsoft and Sun have met 15 times since July, Microsoft director Andrew Layman said. The meetings have included Papadopoulos, Sun CEO Scott McNealy, Microsoft chairman Bill Gates, and Microsoft CEO Steve Ballmer.

Among customers' most urgent requests: making it easier for computer users to get credentials for software that runs on Sun- and Microsoft-powered systems without a lot of extra work; devising Web services that work with both companies' software; making sure Windows runs on 64-bit workstations from Sun that use popular chips from Advanced Micro Devices; getting Sun disk-drive networks to store information from Microsoft's database and E-mail programs; and ensuring that Sun's Java Virtual Machine runs well on Windows.

Especially important, Papadopoulos said, is developing software that lets users log in once to gain access to apps running on Solaris- and Windows-based computers. "We want to make sure this stuff really does work," he said. "I wouldn't be involved at this level, Gates wouldn't be involved at this level, for things that we thought were just standards efforts."

Solving the so-called "single-sign-on" problem has been a thorny one for the computer industry, says Daryl Plummer, an analyst at market researcher Gartner. "Any company of any sufficient size is going to have both Java and Microsoft technology," he says. "When you apply for a mortgage on the Internet or look at payroll and personnel systems to see how much money you have to hire a new person, a lot of systems are involved. You wouldn't want to have to log in to all those systems separately."

But Sun- and Microsoft-based computers handle those log-ons differently and have exploited those differences to push customers to buy more of each company's technology. That means "there's a lot more work for the IT shop to keep it running right," Plummer says. "It's a significant pain point for customers, and it's only going to get worse." Microsoft and Sun will continue to compete, executives from both companies said. But they said the companies' similar approaches to managing intellectual property and research-and-development investment have made it easier to agree on technical matters. Said Papadopoulos: "We're really confident about it."