GSP supports local drives (e.g. C:\media) and networked drives (e.g. \\fileserver\media), but for security reasons it does not support mapped drives (e.g. Z:\media). I assume you can easily specify the UNC path rather than the mapped path.

You specify this path on the Media Objects - General page in the Site admin area. After you do this, you run the synchronize function to import the files into GSP. If any of those files have metadata (keywords, titles, etc), GSP imports them and makes them accessible to the search function. That sounds exactly like what you want.

Note that some programs will assign keywords and other metadata in proprietary ways that GSP can't access. You may want to run a test to make sure your metadata is being extracted as expected.