To add a SharePoint Search Centre service to the list of sources to be searched via Office, you will need to do the following:
1. Open up the Office Application, and then open up the research pane.
2. At the bottom of the Research Pane there will be an option labelled "Research Options". Click on it.
3. In the "Research Options" dialog box, click onthe button labelled "Add Services"
4. This will open another diallog box named "Add Services". In the "Address" text box enter in the URL of your search service.
In SharePoint 2007,this url is http://yoursitenamehere/_vti_bin/Search.asmx
Now users can search MOSS's indexes straight from their Office Application