How to enable Google Drive access for selective set of users, so that they can use the Drive software on their machines to organize data. Rest of the users should just have web access alone.
Unfortunately Drive doesn't yet have the Org. Unit level controls that many of the other Google Apps services do (like Gmail and Calendar), but one option to consider is in Drive > General Settings where you can select "Allow use of Google Drive for Mac/PC, but hide the download links in the Drive interface". You could then distribute the download link to your select users, and at least the rest of your users would never be prompted by Google to download the Drive client.