Microsoft's appeal against the EU's anti-trust ruling is to be judged by Bo Vesterdorf, the president of the Court of First Instance (CFI). Vesterdorf was the judge who in December 2004 threw out Microsoft's attempt to temporarily halt measures imposed by the European Commission.

The news followed the announcement last month that the case would be heard by a Grand Chamber of 13 judges rather than by a five-judge team led by Hubert Legal. The change is expected to lead to a further delay the completion of the case.

Though the court official would not comment on reasons for the change, it is understood to reflect anger at an article by Legal in which he attacked clerks at the court as "ayatollahs of the free market." There had been speculation that Legal, a French national, would stay on as "judge-rapporteur" (reporting judge). The reporting judge is responsible for preparing the court's judgement, including summarising the parties' arguments and drawing the draft final ruling. But the court has decided to appoint Irish judge John Cooke to this position.

Asked how the change would affect the timing of the case, the official said that referring the case to the Grand Chamber would have no direct impact as the case was still in the "written procedure" stage, during which parties make written submissions to the court. He declined to make any further comment about the timing.

However, some parties believe the move will delay the case until the end of 2006 rather than the middle of next year as initially expected. Thomas Vinje, counsel for the European Committee for Interoperable Systems, a group of five tech firms supporting the EU's case, said in June when the proposal to change the judge was first floated that the move could "delay proceedings". Vinje said it was "questionable" whether the 13-judge Grand Chamber would decide as rapidly as Legal's team.

In April 2004 the Commission found Microsoft guilty of abusing the dominant position of its Windows PC operating software to crowd out other vendors. It ordered the company to offer a version of Windows without Windows Media Player and to license its communications protocols for the workgroup server market. It also fined the company €497 million, the largest fine in the EU's history of anti-trust cases.

Microsoft asked for the measures to be suspended pending the outcome of the appeal in the CFI. But CFI President Bo Vesterdorf rejected the request in December 2004, saying that the company had failed to prove that the measures would cause Microsoft "irreparable harm" if they were imposed.

The Commission is considering whether to approve a proposal from Microsoft on how to comply with these measures. It has already indicated that it can accept Microsoft selling a version of Windows without WMP, called Windows XP N, after some changes were made to the program. But the Commission is considering the terms under which Microsoft is prepared to license its communications protocols for workgroup servers. The Free Software Foundation has criticized Microsoft's offer, saying that it imposes unworkable restrictions on their ability to develop products which are interoperable with Microsoft's systems.

The Commission is expected to give its final ruling on whether Microsoft's terms are acceptable before the end of July. If it does not accept them, it can impose fines worth 5 percent of Microsoft's daily turnover until the company comes up with a better offer.