You can do this with a custom Content Type using the Document Content type, and setting a document library to use this content type.
The fields you add to the custom content type (that inherits from Document, remember), will show in the Document Information Panel in Word, and you can add them as Quick Parts in the document. Save it as a template and associate the template with the Document Library.
This way you can create a new file in that library, it'll open with the template - and you can either enter info in the quick parts which will be save to the Content Type Columns when you save the file - or save the file first, update the columns from your content type in the library and open the file to see your quick parts all populated.
Create a site column for each metadata column you want.
Create a custom Content Type which has Document as the parent. Add the site columns you just created.
Create a Document Library. In Advanced Settings, turn on Management of Content Types. Add your custom Content Type.
Upload a starter Word document, and set its content type to your Custom content type. Open this file and the columns should hopefully appear when you add a Quick Part. Save it as a 'template' (.dotx) and associate this with the Document Library through the Library's settings.
Here's a tutorial I've found form a quick google: http://docupoint.wordpress.com/2006/12/08/content-types-document-information-panel-and-quick-parts/
Search around for "SharePoint 2007 Content Types Document Information Panel" to see what other info can be found if you get stuck.