Free copies of some of Microsoft's office software will soon be available.
Many people are turning to online versions of office programs
The software giant said it would make ad-supported copies of the Works package available within "months".
The programs will not run in a web browser but will be installed on a PC and have their cost offset by running adverts while in use.
The move has widely been seen as an attempt by Microsoft to counter the growing number of rivals offering web versions of popular office programs.
Microsoft said the service would debut with Version 9.0 of Works that was due to launch by the end of the year. Word processing and spreadsheet software are expected to be the main part of the package.
The ad-supported version will have a store of adverts it will show to people while they put together documents or spreadsheets. The store of ads would be refreshed every time that computer goes online.
Microsoft has not said which PC makers it is working with on the project who will pre-install the ad-supported copies of Works.
The software company said the trial would run until mid-2008 and was being run to find out if it can generate enough cash to support such a service. The usual retail price of Works in the US is $39.99 (£20).
Microsoft has faced increasing competition in recent years as rivals produce free versions of business software that can be downloaded or used online.
Sun has released the Open Office package of programs and there are many free online packages such as Zoho and Ajax 13.
One of the bigger rivals is Google's web-based Docs and Spreadsheets service that lets people put together and edit these types of files online.
While mainly aimed at individuals, Google also offers an "enterprise" version that comes with technical support to help people use it.
As web technology improves, the gap between the full-featured versions on PCs and the net-based versions will shrink putting more pressure on Microsoft's flagship Office suite of programs.