The European court hearing Microsoft's anti-trust appeal has approved the players that will be able to intervene in the case.

The Court of First Instance (CFI), in Luxembourg, has admitted five organisations in support of Microsoft and four in support of the European Commission.

Those arguing for Microsoft include industry trade groups and long-time allies the Association for Competitive Technology (ACT) and Computing Technology Industry Association (CTIA). Also speaking on its behalf are European companies Exorof Sweden, small business software provider Mamut of Norway and Italian enterprise software provider Teamsystem. Mamut and Teamsystem represent one intervening organisation, acting together with combined legal representation.

The fifth intervenor for Microsoft is the group consisting of digital rights management software vendor DMD Secure.com, MPS Broadband, digital TV set-top box technology company Pace Micro Technology, digital technology provider Quantel. and Tandberg Television.

In the Commission's corner is long-time Microsoft rival RealNetworks, as well as Free Software Foundation Europe, Software and Information Industry Association (SIIA) and Audiobanner.com trading as Videobanner, which uses streaming audio and video in advertising banners.

Absent from the list are previous Microsoft opponents Novell and the Computer and Communications Industry Association (CCIA). The software giant reached settlements with both organisations last year.

The intervenors will provide live testimony and written observations as the court deliberates over an appeal of the sanctions levelled against the software maker last year. Only organisations that could prove the outcome of the case would have a direct impact on their business were admitted as intervenors.

The Commission decided last March that Microsoft abused its dominance in the desktop software market in order to gain an edge in related markets, most notably media players, where its competitors include Apple Computer and RealNetworks. The Commission hit the company with a €497 million (£346 million) fine, ordered it to release in Europe a version of the Windows operating system without its Windows Media Player (WMP) and publish APIs for its workgroup server software.

Microsoft was denied a request late last year to suspend the sanctions until the full appeal was heard and the company is currently is the process of complying.