Microsoft is preparing to return to court in the US to challenge an earlier decision that it has hampered competition by weaving its internet browser and Windows operating system together.

In a move which legal experts suspect is a delaying tactic, the software company has asked a US appeals court to re-examine the ruling that it has illegally "co-mingled" the computer code to Explorer with Windows.

The challenge risks reopening one of America's most high-profile lawsuits but, if successful, could allow the company free rein to launch its next generation Windows this autumn.

Last month the US court of appeals for the District of Columbia overturned an earlier ruling that Microsoft must be split into two separate companies.

However, the court, which condemned the original trial judge Judge Thomas Penfield Jackson for his handling of the case, did rule that Microsoft has engaged in "exclusionary conduct" by bundling its browser together with Windows.

Microsoft is requesting a rehearing, saying that "a full review of the record establishes that there is no foundation to sustain the conclusion, and that further review of this issue is in the best interest of the law, of the technology industry and of consumers".

The news came as Microsoft's web portal MSN announced a link-up with online banking business Egg. The deal will give the UK-based financial services company a springboard into western Europe. MSN's European websites receive about 42m unique visitors each month.

Egg's chief executive Paul Gratton said the company is planning a pilot scheme in the UK which will be launched towards the end of the year. A full service for UK visitors to MSN will be launched next spring. Beyond that, Mr Gratton said Egg, which was floated by Prudential in June last year, would start to offer financial services across mainland Europe.