I was able to do this in Windows XP Search and using something like Copernicus.
I don't see any way to do this with Windows 7 (other than making it available offline which means that all that data will be duplicated on my local drive.
What I've tried : I read elsewhere in the Windows 7 Help that you need to make sure the networked drive is indexed by it's O/S. So this network drive is on our Server (XP Pro, SP3) so I've installed Windows Search 4.0 and set it to indexing that drive.
I have another XP machine which is already indexed and Windows 7 still wouldn't let me add that drive to a Library (to get it indexed) because it's not indexed. So I'm not hopeful that the above solution will work.