If Microsoft had its way, that'd be one software vendor per child.
The One Laptop Per Child (OLPC) program, led by Nicholas Negroponte, is hoping to deliver budget laptops around the world to keep even low-income people abreast of modern technology and to allow them to leverage high tech to improve their lives. OLPC is, in essence, about trying to maintain the possibility of modern education in a world of scarce resources; it is an idealistic effort to provide the tools needed to make sure children can learn to use the tools that make the future possible.
Microsoft's efforts to get pre-installed status on the XO haven't been exactly smooth. OLPC, after all, reportedly rebuffed a no-fee offer by Apple to license MacOS X (whose open-source kernel is derived from the FreeBSD project to which Apple is a contributor, and the Mach project which Apple's retired Avadis Tevanian had nursed at MIT), purportedly because of non-open-source code also involved in MacOS X made the system politically unsatisfactory to OLPC. But apparently you can buy satisfaction. Microsoft, apparently concerned about a future in which discount laptops around the world would obsolete its proprietary file formats and render its high-margin products irrelevant, poured significant resources into a version of Microsoft-Windows designed to run on XO. Microsoft has insinuated its products into the OLPC program, even to the point of causing hardware modifications in OLPC in order to allow its enormous code to be stored and run on the machines. The fact that retail buyers in the US are not yet assured the ability to buy XO with pre-installed Microsoft products is of little concern to either Microsoft (which assumes you as an American can afford a costlier copy, and will do so on your next computer purchase) or OLPC (which is trying to look like an Open-Source advocate).
The fact that towns in Columbia have begun deploying Microsoft-Windows-equipped XO machines in schools (at least in part on Microsoft's nickel, hence the product placement opportunity) suggests that OLPC hasn't really stuck to its principled stance that recipients need to enjoy the Four Freedoms when they use and study software. OLPC is more interested in keeping its own project from becoming irrelevant through lack of funding. And there, OLPC and Microsoft can find common ground.