Rebuffed at the time, Gutierrez in May sought information on potential plug-ins from third-party software vendors. Sun and five smaller ISVs responded.

A Belgian officials praised the Microsoft move. "This is an important commitment regarding software interoperability. Hence, we're extremely pleased by this announcement by Microsoft," said Peter Vanvelthoven, Belgian minister of employment and computerization. Belgium approved the use of ODF June 23, but said it will also use Microsoft's OpenXML format if it is accepted as a standard by ISO.

The three firms working on the Microsoft-sponsored plug-in -- Paris-based Clever Age, which has written most of the code thus far, India's AztecSoft, which will test it, and Germany's Dialogika, which will test and help implement the finished product -- were not among the respondents to Massachusetts.

According to Paoli, Clever Age approached Microsoft last year after some initial development. "They started having good results, so we asked them to continue," he said.

Microsoft is providing an undisclosed amount of money to the three firms creating the plug-in, which is expected to let users convert multiple files at the same time.