"We are still committed to the existing plan of record."
Microsoft plans to release Vista to business customers in November before a wider general release by January.
The European Commission fined Microsoft 280.5 million euros ($356.6 million) on Wednesday for defying a 2004 antitrust ruling in which it ordered Microsoft to give rivals information that would enable their servers to compete on a level playing field with Microsoft's by interconnecting smoothly with Windows.
It also found that Microsoft harmed competitors by illegally bundling its Windows Media Player with the operating system, leaving consumers little incentive to buy rival software to watch movies or listen to music.
The bundling issue has raised concerns about Vista, which could package Internet search functions or software that creates fixed documents and thus threaten Google Inc. and Adobe Systems Inc. .
Any change in the timing of Vista's launch could have a substantial impact on global demand for personal computers and key PC components such as microchips.
The new penalty by the commission comes on top of a record 497 million euro fine it imposed in a landmark antitrust decision against it in March 2004.