Microsoft witness Joachim Kempin made the courtroom a frustrating place to be on Feb. 25 -- especially for lead Justice Dept. litigator Davis Boies and presiding Judge Thomas Penfield Jackson. Microsoft lawyers and public relations crew weren't smiling either, as Kempin took the courtroom on a wild semantic roller-coaster ride.

In more than five hours of cross-examination, Kempin, Microsoft's senior vice-president for computer sales, contradicted his own sworn testimony repeatedly, as well as his sworn depositions from October, 1997. For Boies, proving a point in court was like pulling a tooth.

At one spot, Boies sarcastically asked Kempin, a native of Germany who has worked for Microsoft in Washington State for more than a dozen years, what language he speaks at work.

"Most of the time my business is in English," Kempin answered. "but sometimes I speak French and German."

"When you write E-mails, English is the language you use, correct?" Boies pressed on.

"Well, not always," Kempin said.

Boies wouldn't be denied. "What about when you write to the executives of Microsoft?," he said, running down a list of prominent American surnames.

"English," Kempin finally allowed. It was that kind of day.

STICKY MOMENT. Kempin said his testimony was repeatedly changing because he was having "a hard time understanding the questions" Boies posed. But the Justice litigator was clearly annoyed at Kempin's performance on the witness stand. Boies later told reporters that the executive is "one of the smartest men working at Microsoft"

During one of Kempin's stickier moments of cross-examination, Boies caught him contradicting an answer to a question he had asked the Microsoft exec 10 minutes earlier. Boise wanted to know if a huge manufacturer such as Acer or Gateway could feature a browser other than their own and that of Microsoft. Netscape's, for instance.

"Yes," Kempin said. "If they want to list a third browser, that's O.K. They can do that."

Trouble was, moments before, Kempin had said the Microsoft license agreement "doesn't allow that." And later he would say Gateway computers had to be given special oral permission to include a third browser.

Confused? Boies and Judge Jackson were, too. As the grilling got hotter, Boies tried to get Kempin to give the court an estimate of how many PCs ship Netscape Navigator as their browser. Kempin said no estimates had ever been compiled. Then he added that he is "probably too German to answer that" without data. Later, still, Kempin said a figure did in fact exist, but he knew that only because other computer makers had told him. The judge sighed and said, "You were very reluctant to give us any estimate because you have no data, and now you're telling me you have heard another by word of mouth?

"MAJOR ISSUE." When Boies got the chance to move into substance of the antitrust allegations against Microsoft, he set out to show that Microsoft had skirted a 1995 consent decree with the government through a deal with Compaq.

Under the consent decree, companies with existing contracts with Microsoft were given an option other than just renewing them. Under those existing contracts, companies were bound to purchase Windows 95 software for each processor -- regardless of whether the operating system was installed on the machine. But the consent decree allowed companies to purchase the system on a per-copy basis.

Boies presented portions of a sealed document before court broke containing internal Compaq documents discussing the deal. The documents said that when Compaq inquired about the new option, Microsoft told the company if it took the deal "it would be viewed as a major issue at Microsoft." In the end, Compaq renewed its per-processor agreement. Boies inferred that Microsoft was bullying Compaq to ignore the option made available in the 95 consent decree.

Kempin said he had no idea of the negotiations but figured Compaq just didn't want to rewrite the whole contract.

Talk of contracts wove in and out of the testimony all day, as Kempin first affirmed and then refuted agreements Microsoft had made with computer manufacturers when they "tampered" with Microsoft's product. In one case, Kempin was asked about incentive programs to stop PC makers from altering Microsoft code. The software giant offered to help PC manufacturers market their products if they adhered to the strict lines of Microsoft's licensing agreement.

"I hope this isn't a memory test," Kempin said when asked about the agreement he could not recall at first. "I have nothing to hide."

Moments later he acknowledged the deals, declaring that he had "suddenly remembered" and called them a "very generous gesture" to the PC makers.

Boies offered as evidence a January, 1996, E-mail from Microsoft CEO Bill Gates to Kempin in which Gates stressed, "Winning Internet browser share is a very, very important goal for us." Boies asked, "In January, 1996, who were the other competing browsers?"

Kempin said there were many, and identified a few he knew of. But Boies persisted. "Prominent browsers, Mr. Kempin?"

"Only Netscape," Kempin answered. And it is Microsoft's alleged targeting of the browser produced by Netscape that's at the heart of the Justice case.

Kempin is expected to retake the witness stand on Friday, Feb. 26, for more cross-examination by Boies.

By Mica Schneider in Washington