There are many applications like openoffice.org, Google Docs and other free and open source office applications. Files created in these applications have file extensions has .ODT (text document) .ODS (spreadsheet) and .ODP (PowerPoint). Files with these extensions will not open in Microsoft Office 2007 or earlier versions. But you can make them open in MS Office by installing a plug-in.

You can download and install Sun ODF plug-in for Microsoft Office by clicking on the link here. If this is the first time you are downloading any software from Sun then you need to registry with the site and download Sun downloader.

Follow on screen instruction to finish registration and download the Sun ODF plug-in for Microsoft Office. Now you need to unpack the Windows installer file and proceed installing the plug-in using Windows installer by double clicking on the file.

Once you have successfully installed the plug-in it gets integrated with MS Office such that you can view any .odf files in MS office.