Windows Vista Search is an extremely powerful way to find the files your looking for. However sometimes your looking for a file or document that may have a generic name, for instance Report*.doc. (or docx in the newer Word 2007)
Vista solves these kinds of situations by allowing you to tag your documents with meta data. Meta Data is simply data about data. to add MetaData to a file simply right click on the file then choose the Details tab.

This meta data can then be used to narrow down searches.

You can add several tags to your document. The Meta Data is indexed in real time. If you leave a search dialog box with a tag that you haven't added to a file in the search field, simply adding this Tag to a file will cause it to appear in the search dialog.
The next time your looking for "that" specific file just you'll have an extra bit of information that you can use to search.