Microsoft has commenced its legal fightback against the greater than $600 million fine it was handed by the European Commission in 2004 for alleged anti-competitive practices.

Much of the ruling hinged upon Microsoft’s integration of Media Player in the Windows operating and the software company allegedly with-holding interoperability information from competing developers of work group software, which would enable their products to work with Windows properly.

The European Commission ruled that Microsoft had illegally used its monopoly to stifle innovation in the marketplace, a charge that Microsoft denies and intends to get reversed in the European Court of First Instance in Luxembourg, the second highest court in the EU.

All agree that the stakes are high for both parties. In Microsoft’s case, if it loses the challenge it could well find itself mired in further expensive anti-competition cases, which to date have already the company more than $1 billion in settlements and legal charges.As far as the European Commission is concerned, its credibility as a regulator is on the line.