SEATTLE, US - Microsoft Corp, reached an agreement to make available its Windows operating system software for the One Laptop Per Child Foundation's XO Laptop, the company said on Thursday.

Microsoft was not part of the project started by Massachusetts Institute of Technology professor Nicholas Negroponte to develop an inexpensive laptop computer for elementary school children in developing countries.

In recent months, the two sides have engaged in more serious talks and started testing the XO Laptop's Sugar software package on Microsoft's Windows operating system, which runs on more than 90 percent of the world's computers.

Microsoft said it plans to start trials of Windows on the low-cost laptop in key emerging markets as early as June. Customers will be able to choose to run the computer on either a Windows or a Linux operating system.

Sugar was designed only to work with a free Linux operating system that engineers from Red Hat Inc. Eventually, the goal will be to develop versions of the laptop to run both Linux and Windows, leaving the user to decide which operating system to run when the machine boots up, Negroponte said.

Sugar is a suite of educational software that includes a user interface for the green-and-white machines with a display that switches from color to black-and-white for viewing in direct sunlight.