for a video explaining the usage. You can use the builtin export functionality for Office 2007 xml format, which is the format in which Microsoft stores it bibliography information.
Export (selected) entries in JabRef and choose Office 2007 xml format
Open Word, click on the References Tab
Click on Manage sources -> Browse -> Open the exported XML File (or better copy it directly to the location under browse)
All entries are then available in the MS bibliography database
For a detailed list of the fields which are exported in the Office 2007 xml format see the following page.