After months of nibbling at the edges, government attorneys struck at the heart of a key Microsoft demonstration this morning, stopping just short of accusing Microsoft Senior Vice President James Allchin of falsifying a presentation even Microsoft says is key to its defense. The confrontation arose from a videotape presented in court yesterday. During that presentation, Microsoft executive Yusuf Mehdi seemingly showed that a prototype government program designed to disable the browser within Windows 98 drastically slowed the functioning of the operating system once it had been installed. Microsoft lawyers have used that demonstration to argue against intervention to keep them from bundling their browser with the operating system. But in what was probably the most dramatic confrontation to date, government attorney David Boies showed that the tape, whose preparation Allchin had supervised, wasn't what it was supposed to be. "You do understand that you came in here and you swore that this was accurate. You know it does matter whether what you say here is right or wrong. You know that matters, don't you?" an accusatory Boies asked Allchin. "What's on the screen," Allchin replied simply, "is the truth." During their presentation, Microsoft executives showed how, even after the Felten program had been installed, they could get to the company's Windows update service on the Web. But they also seemed to show how that service -- one which Felten testified he left in place intentionally -- functioned two to three times slower. Yet there, at the top of the browser window, was a telltale sign that not all was as advertised -- instead of the title "Windows 98," which appears at the top of the Felten version of Windows, were the words: "Internet Explorer." Boies asked how Allchin could claim the Felten program made Windows run more slowly when the screen seemed to show the Felten program wasn't present. Oops! Allchin said he didn't know. "From what I'm seeing here," he said, "they filmed the wrong system." Boies continued to work the point. "It's not because of the Felten program," he said, that the Web site was taking so long. "It's because of the way Windows runs." "How in the world could people have run this program calling it the Felten program when obviously they knew it wasn't?" Boies asked. "They probably just filmed it several times and they probably grabbed the wrong tape," Allchin replied. "I didn't worry about having to go supervise every bit of this," he added. "To a certain extent, it doesn't matter. This problem still exists." The executive said he stood behind earlier written testimony in which he claimed Windows displayed documents based on popular Internet standards two to seven times slower once the Felten program had been installed. Though Allchin later conceded several programs were present on the computers used in the demonstration that were not used for his own tests, he insisted those programs had nothing to do with the slow performance shown in court. Later in the day, Boies presented Allchin with a March, 1997 e-mail in which the computer scientist told other senior officials that he thought the company should move its IE browser out of the operating system entirely and make it a "plug-in" like any other freestanding application in order to speed development of the forthcoming Windows 98, known then as Memphis. Microsoft has said throughout the trial it decided to build its IE browser into the operating system as early as 1994. Company attorneys have also said the browser became inextricably linked to the operating system as early as 1995. "Move the shell -- but not the browser -- to the (operating system) team," he wrote to a group of senior executives. "This was my recommendation before as you know. It may not be the thing for other reasons, but it is the right thing to do for the OS (both Memphis and NT). IE 4 would just plug into the environment." Boies asked Allchin how he could recommend separating the two if they were, indeed, inseparable. "That was just plain wrong," he said of the memo. Back then, he explained, he had not realised how monumental the task of separating the two would be. After court had adjourned for the day, Microsoft spokesman Mark Murray said the company stood behind its original position that the Felten removal program slows Windows. "The machine that was shown in Microsoft's video was, in fact, a machine on which the government's program had disabled certain aspects of Windows 98," he said. Though it remained unclear why the browser on the videotape bore the banner "Internet Explorer," rather than "Windows 98," he said, engineers at Redmond, Wash., headquarters were continuing to probe the computer they used for the demonstration. Microsoft Sr. Vice President for Law and Corporate Affairs Bill Neukom said his legal team might submit a new, audited demonstration into evidence, but no decision had been made. "To the extent that we are able to learn more about that, we will introduce that into the record," he said. Boies, who earlier seemed so ferocious in court, downplayed earlier reports that he had accused the company of falsifying evidence. "I'm not suggesting something nefarious happened in Redmond," Boies insisted. "All we know is the tape they put into evidence is not reliable." He also shied away from accusing Allchin himself of lying. "I have no reason to believe that Mr. Allchin is anything other than someone who made a mistake in relying on other people."